The aim of this study was to determine the association between dietary intake, determined using a food frequency questionnaire, and genome damage in lymphocytes measured using the micronucleus (MN) assay. The study, performed on 190 healthy individuals (mean age 47.8 years, 46% males), also examined whether a supplementation with beta-carotene, vitamins C and E along with zinc (ACEZn), in a randomized trial for 6 months, improves genome stability. Multivariate analysis of baseline data showed that (1) the highest tertile of intake of vitamin E, retinol, folic acid, nicotinic acid (preformed) and calcium is associated with significant reductions in MN frequency, i.e. -28, -31, -33, -46 and -49%, respectively (P < 0.005) relative to the lowest tertile of intake and (2) the highest tertile of intake of riboflavin, pantothenic acid and biotin was associated with significant increases in MN frequency, i.e. +36% (P = 0.054), +51% (P = 0.021), and +65% (P = 0.001), respectively, relative to the lowest tertile of intake. Mid-tertile beta-carotene intake was associated with an 18% reduction in MN frequency (P = 0.038); however, the highest tertile of intake (>6400 microg/day) resulted in an 18% increment in MN frequency. Supplementation with ACEZn significantly reduced the MN index by 13% (P = 0.038). The study also showed interactive additive effects such as the protective effect of increased calcium intake (-46%) and the exacerbating effect of riboflavin (+42%) on increased genome damage caused by low folate intake. The results from this study illustrate the strong impact of a wide variety of micronutrients and their interactions on genome health, depending on the level of intake.

Keratoconus (KCN) is an ectatic disorder with progressive corneal thinning and a clinical picture of corneal protrusion, progressive irregular astigmatism, corneal fibrosis and visual deterioration. Other ectatic corneal disorders include: post-LASIK ectasia (PLE) and pellucid marginal degeneration (PMD). Corneal crosslinking (CXL) is a procedure whereby riboflavin sensitization with ultraviolet A radiation induces stromal crosslinks. This alters corneal biomechanics, causing an increase in corneal stiffness. In recent years, CXL has been an established treatment for the arrest of KCN, PLE and PMD progression. CXL has also been shown to be effective in the treatment of corneal infections, chemical burns, bullous keratopathy and other forms of corneal edema. This is a current review of CXL - its biomechanical principles, the evolution of CXL protocols in the past, present and future, indications for treatment, treatment efficacy and safety.

Flavin reductases use flavins as substrates and are distinct from flavoenzymes which have tightly bound flavins. The reduced flavin can serve to reduce ferric complexes and iron proteins. In Escherichia coli, reactivation of ribonucleotide reductase is achieved by reduced flavins produced by flavin reductase. The crystal structure of E. coli flavin reductase reveals that the enzyme structure is similar to the structures of the ferredoxin reductase family of flavoproteins despite very low sequence similarities. The main difference between flavin reductase and structurally related flavoproteins is that there is no binding site for the AMP moiety of FAD. The direction of the helix in the flavin binding domain, corresponding to the phosphate binding helix in the flavoproteins, is also slightly different and less suitable for phosphate binding. Interactions for flavin substrates are instead provided by a hydrophobic isoalloxazine binding site that also contains a serine and a threonine, which form hydrogen bonds to the isoalloxazine of bound riboflavin in a substrate complex.

Lycium barbarum has been used in China for more than 2,000 years as a traditional medicinal herb and food supplement. Lycium barbarum contains abundant Lycium barbarum polysaccharides (LBPs), betaine, phenolics, carotenoids (zeaxanthin and β-carotene), cerebroside, 2-O-β-d-glucopyranosyl-l-ascorbic acid (AA-2βG), β-sitosterol, flavonoids and vitamins (in particular, riboflavin, thiamine, and ascorbic acid). LBPs are the primary active components of Lycium barbarum. In this review, we discuss the pharmacological activities of LBPs and other major components. They have been reported to mediate significant anti-aging effects, through antioxidant, immunoregulative, anti-apoptotic activities and reducing DNA damage. Thus, the basic scientific evidence for anti-aging effects of LBPs is already available. However, additional studies are needed to understand mechanisms by which LBPs mediate anti-aging properties. Novel findings from such studies would likely pave the way for the clinical application of traditional chinese medicine Lycium barbarum in modern evidence-based medicine.

Micronutrient deficiencies and low dietary intakes among community-dwelling older adults are associated with functional decline, frailty and difficulties with independent living. As such, studies that seek to understand the types and magnitude of potential dietary inadequacies might be beneficial for guiding future interventions. We carried out a systematic review following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement. Observational cohort and longitudinal studies presenting the habitual dietary intakes of older adults (≥65 years) were included. Sex-specific mean (and standard deviation) habitual micronutrient intakes were extracted from each article to calculate the percentage of older people who were at risk for inadequate micronutrient intakes using the estimated average requirement (EAR) cut-point method. The percentage at risk for inadequate micronutrient intakes from habitual dietary intakes was calculated for twenty micronutrients. A total of thirty-seven articles were included in the pooled systematic analysis. Of the twenty nutrients analysed, six were considered a possible public health concern: vitamin D, thiamin, riboflavin, Ca, Mg and Se. The extent to which these apparent inadequacies are relevant depends on dynamic factors, including absorption and utilisation, vitamin and mineral supplement use, dietary assessment methods and the selection of the reference value. In light of these considerations, the present review provides insight into the type and magnitude of vitamin and mineral inadequacies.

Anemia affects one-quarter of the world's population, but its etiology remains poorly understood. We determined the prevalence of anemia and studied underlying risk factors in infants (6-23 months), young school-aged children (6-8 years), and young non-pregnant women (15-25 years) in south-central Côte d'Ivoire. Blood, stool, and urine samples were subjected to standardized, quality-controlled methods. We found high prevalence of anemia, malaria, inflammation, and deficiencies of iron, riboflavin, and vitamin A but low prevalence and intensities of soil-transmitted helminth and schistosome infections. Multivariate regression analysis revealed significant associations between anemia and Plasmodium falciparum for infants, inflammation for school-aged children, and cellular iron deficiency for both school-aged children and non-pregnant women. Women with riboflavin deficiency had significantly lower odds of anemia. Our findings call for interventions to protect infants from malaria, improved intake of dietary iron, better access to health care, and health education.

Relations between diet and nuclear opacities in the lens of the eye were investigated in a population-based cohort of middle-aged and older adults who lived in Beaver Dam, Wisconsin. Nuclear sclerosis was assessed from photographs of the lens taken during 1988-1990 in 1,919 persons in the Beaver Dam Eye Study. Diets in the past (1978-1980) were assessed retrospectively with the use of a food frequency questionnaire in home interviews. Relations with intake of foods and nutrients were evaluated using logistic regression analyses. In men, after controlling for age, smoking, and heavy drinking, intakes of numerous nutrients in the highest versus lowest quintile were associated with 40-50 percent reduced odds of more severe nuclear sclerosis. Relations with some nutrients (vitamins A, C, and E, riboflavin, thiamin, niacin) were at least partly explained by previously identified inverse associations with multivitamin use. Relations with other nutrients (folate, alpha-carotene, and dietary fiber) appeared to reflect associations with intake of foods, particularly vegetables. Inverse associations with individual nutrients and foods were often weaker or nonexistent in women. These data indicate that the intake of vitamin supplements (in men and women) and certain foods (particularly in men) may explain associations of several nutrients with risk for nuclear sclerosis.

The present review focuses on the B-vitamins, i.e. folate, vitamin B12, vitamin B6 and riboflavin, that are involved in homocysteine metabolism. Homocysteine is a S-containing amino acid and its plasma concentrations can be raised by various constitutive, genetic and lifestyle factors, by inadequate nutrient status and as a result of systemic disease and various drugs. Hyperhomocysteinaemia is a modest independent predictor of CVD and stroke, but causality and the precise pathophysiological mechanism(s) of homocysteine action remain unproven. The predominant nutritional cause of raised plasma homocysteine in most healthy populations is folate insufficiency. Vitamin B12 and, to a lesser extent, vitamin B6 are also effective at lowering plasma homocysteine, especially after homocysteine lowering by folic acid in those individuals presenting with raised plasma homocysteine. However, riboflavin supplementation appears to be effective at lowering plasma homocysteine only in those individuals homozygous for the T allele of the C677T polymorphism of the methylenetetrahydrofolate reductase (MTHFR) gene. This gene codes for the MTHFR enzyme that produces methyltetrahydrofolate, which, in turn, is a substrate for the remethylation of homocysteine by the vitamin B12-dependent enzyme methionine synthase. Individuals with the MTHFR 677TT genotype are genetically predisposed to elevated plasma homocysteine, and in most populations have a markedly higher risk of CVD.

The aim was to review the published literature on corneal collagen cross-linking. The emphasis was on the seminal publications, systemic reviews, meta-analyses and randomized controlled trials. Where such an evidence did not exist, selective large series cohort studies, case controlled studies and case series with follow-up preferably greater than 12 months were included. Riboflavin/Ultraviolet A (UVA) corneal collagen cross-linking appears to be the first treatment modality to halt the progression of keratoconus and other corneal ectatic disorders with improvement in visual, keratometric and topographic parameters documented by most investigators. Its precise mechanism of action at a molecular level is as yet not fully determined. Follow-up is limited to 4-6 years at present but suggests continued stability and improvement in corneal shape with time. Most published data are with epithelium-off techniques. Epithelium-on studies suggest some efficacy but less than with the epithelium-off procedures and long-term data are not currently available. The use of Riboflavin/UVA CXL for the management of infectious and non-infectious keratitis appears very promising. Its use in the management of bullous keratopathy is equivocal. Investigation of other methodologies for CXL are under investigation.

BACKGROUND

No available treatments slow or halt progression of multiple system atrophy, which is a rare, progressive, fatal neurological disorder. In a mouse model of multiple system atrophy, rifampicin inhibited formation of α-synuclein fibrils, the neuropathological hallmark of the disease. We aimed to assess the safety and efficacy of rifampicin in patients with multiple system atrophy.

METHODS

In this randomised, double-blind, placebo-controlled trial we recruited participants aged 30-80 years with possible or probable multiple system atrophy from ten US medical centres. Eligible participants were randomly assigned (1:1) via computer-generated permuted block randomisation to rifampicin 300 mg twice daily or matching placebo (50 mg riboflavin capsules), stratified by subtype (parkinsonian vs cerebellar), with a block size of four. The primary outcome was rate of change (slope analysis) from baseline to 12 months in Unified Multiple System Atrophy Rating Scale (UMSARS) I score, analysed in all participants with at least one post-baseline measurement. This study is registered with ClinicalTrials.gov, number NCT01287221.

RESULTS

Between April 22, 2011, and April 19, 2012, we randomly assigned 100 participants (50 to rifampicin and 50 to placebo). Four participants in the rifampicin group and five in the placebo group withdrew from study prematurely. Results of the preplanned interim analysis (n=15 in each group) of the primary endpoint showed that futility criteria had been met, and the trial was stopped (the mean rate of change [slope analysis] of UMSARS I score was 0.62 points [SD 0.85] per month in the rifampicin group vs 0.47 points [0.48] per month in the placebo group; futility p=0.032; efficacy p=0.76). At the time of study termination, 49 participants in the rifampicin group and 50 in the placebo group had follow-up data and were included in the final analysis. The primary endpoint was 0.5 points (SD 0.7) per month for rifampicin and 0.5 points (0.5) per month for placebo (difference 0.0, 95% CI -0.24 to 0.24; p=0.82). Three (6%) of 50 participants in the rifampicin group and 12 (24%) of 50 in the placebo group had one or more serious adverse events; none was thought to be related to treatment.

CONCLUSIONS

Our results show that rifampicin does not slow or halt progression of multiple system atrophy. Despite the negative result, the trial does provide information that could be useful in the design of future studies assessing potential disease modifying therapies in patients with multiple system atrophy.

BACKGROUND

National Institutes of Health, Mayo Clinic Center for Translational Science Activities, and Mayo Funds.

BACKGROUND

Fusarium head blight (FHB) caused by Fusarium graminearum Schwabe is one of the most prevalent diseases of wheat (Triticum aestivum L.) and other small grain cereals. Resistance against the fungus is quantitative and more than 100 quantitative trait loci (QTL) have been described. Two well-validated and highly reproducible QTL, Fhb1 and Qfhs.ifa-5A have been widely investigated, but to date the underlying genes have not been identified.

RESULTS

We have investigated a gene co-expression network activated in response to F. graminearum using RNA-seq data from near-isogenic lines, harboring either the resistant or the susceptible allele for Fhb1 and Qfhs.ifa-5A. The network identified pathogen-responsive modules, which were enriched for differentially expressed genes between genotypes or different time points after inoculation with the pathogen. Central gene analysis identified transcripts associated with either QTL within the network. Moreover, we present a detailed gene expression analysis of four gene families (glucanases, NBS-LRR, WRKY transcription factors and UDP-glycosyltransferases), which take prominent roles in the pathogen response.

CONCLUSIONS

A combination of a network-driven approach and differential gene expression analysis identified genes and pathways associated with Fhb1 and Qfhs.ifa-5A. We find G-protein coupled receptor kinases and biosynthesis genes for jasmonate and ethylene earlier induced for Fhb1. Similarly, we find genes involved in the biosynthesis and metabolism of riboflavin more abundant for Qfhs.ifa-5A.

Riboflavin, a water-soluble vitamin also known as vitamin B2, is essential for normal cellular functions. Riboflavin transporters play important roles in its homeostasis. Recently, three novel riboflavin transporters were identified, and designated as RFT1, RFT2 and RFT3. Because the RFTs did not show similarity to other SLC transporters, and RFT1 and RFT3 are similar in sequence and function, they were assigned into a new SLC family, SLC52. Subsequently, RFT1/GPR172B, RFT3/GPR172A and RFT2/C20orf54 were renamed as RFVT1/SLC52A1, RFVT2/SLC52A2 and RFVT3/SLC52A3, respectively. In this review, we summarize recent findings on the cloning, nomenclature, functional characterization and genetic diseases of RFVT1/SLC52A1, RFVT2/SLC52A2 and RFVT3/SLC52A3.

Receptors that transport vitellogenin (VTG) into oocytes are of vital importance to egg-laying species, because they mediate a key step of oocyte maturation, a prerequisite to reproduction. Vitellogenins are lipophosphoglycoproteins that are produced under female hormonal control in large central organs (fat body in insects; liver in higher animals) and are transported in the circulation to the female gonads. VTG receptors localized in coated pits on the surface of growth-competent oocytes are able to accumulate in the yolk high concentrations of VTG and other ligands they recognize. The study of VTG receptors and their ligands has identified genes that specify related ligands, and a family of receptors. To date, all molecularly characterized VTG receptors belong to the low-density lipoprotein receptor supergene family, which ranges from a 600-kDa receptor in Caenorhabditis elegans to the 100-kDa so-called very-low-density lipoprotein receptors in mammals. These receptors, by and large, recognize ligands with similarities in structural elements first defined in the human apoplipoproteins B-100 and E. Recent studies on the receptor family have added VTG and lipoprotein lipase to the list of co-evolved ligands and have revealed that VTG receptors are able to interact with ligands other than VTG and also with some unrelated to lipoprotein metabolism. For example, the chicken VTG receptor also imports very-low-density lipoprotein, riboflavin-binding protein, and alpha-2-macroglobulin into growing oocytes. Such multifunctionality of receptors is likely the result of evolutionary pressure to provide the female germ cell with a highly economical machinery for vitellogenesis.

Evidence of the impact of maternal nutritional status on pregnancy outcome is increasing. However, reference values for vitamin and homocysteine concentrations in maternal blood during normal pregnancy are scarce, and are lacking for the preconceptional period and early pregnancy. Thus, in a longitudinal study we evaluated vitamin and homocysteine concentrations in 102 nulliparous women with an uneventful singleton pregnancy and normal outcome not using supplements. The physiological changes in vitamin and homocysteine concentrations in blood were determined from the preconceptional period throughout pregnancy until 6 weeks post-partum. The vitamins evaluated comprised retinol, thiamin, riboflavin, pyridoxal 5'-phosphate, folate in serum and erythrocytes, vitamin B12 and alpha-tocopherol. The plasma homocysteine concentration was also measured, considering the essential roles of folate, vitamin B6 and vitamin B12 in homocysteine metabolism. The concentrations of retinol, thiamin, pyridoxal 5'-phosphate serum folate and vitamin B12 decreased during pregnancy. In contrast, the concentrations of riboflavin, alpha-tocopherol, and folate in erythrocytes increased or showed only minor changes. Homocysteine concentrations also remained approximately constant during pregnancy. These observations emphasize the importance of preconceptional and post-partum concentrations of vitamins in the evaluation of pregnancy-induced changes. These data have provided valuable reference values for vitamins and homocysteine before, during and after pregnancy in order to contribute to better diagnosis of maternal deficiencies and to study further the relationship between maternal vitamin status and adverse course and outcome of pregnancy.

A population-based case-control study of esophageal cancer (902 cases, 1,552 controls) in Shanghai, China, investigated the etiologic role of diet. After adjustment for cigarette smoking, alcohol consumption and other risk factors, increasing consumption of fruits, dark orange vegetables and beef or mutton was associated with statistically significant decreasing trends in risk for esophageal cancer. In general, risks were about 40% lower among those in the upper vs. lower quartiles of intake of these foods. Fivefold increases in risk were observed among those who consumed burning hot soup or porridge, with smaller excesses for preserved vegetables, salty and deep fried foods. Nutrient analysis revealed that increased dietary intake of protein, carotene, vitamins C and E and riboflavin was associated with reduced esophageal cancer risk. Our findings support the notion that the reported temporal increases in the per capita consumption of fruits, vegetables and animal products contribute to the substantial reduction in the incidence of esophageal cancer in Shanghai, particularly since cigarette and alcohol use has not decreased.

BACKGROUND

Koko, a fermented maize porridge used as the primary complementary food in Ghana, has been implicated in the high prevalence of child malnutrition. Weanimix, a cereal-legume blend developed by the United Nations Children's Fund and the Ghanaian government, has been promoted as an alternative.

OBJECTIVE

We evaluated the effect of feeding Weanimix and 3 other locally formulated, centrally processed complementary foods on the nutritional status of 208 breast-fed infants.

METHODS

Infants were randomly assigned to receive 1 of 4 foods from 6 to 12 mo of age: Weanimix (W), Weanimix plus vitamins and minerals (WM), Weanimix plus fish powder (WF), and koko plus fish powder (KF). Dietary and anthropometric data were collected regularly. Blood was collected at 6 and 12 mo of age to assess iron, zinc, vitamin A, and riboflavin status. Before and after the intervention, cross-sectional data on the anthropometric status of infants not included in the intervention (NI; n = 464) were collected.

RESULTS

There were no significant differences between intervention groups in weight or length gain or in hemoglobin, hematocrit, transferrin saturation, plasma zinc, or erythrocyte riboflavin values between 6 and 12 mo of age. From 9 to 12 mo of age, z scores were lower in NI infants than in the combined intervention groups [at 12 mo: -1.71 +/- 0.90 compared with -1.19 +/- 0.93 for weight and -1.27 +/- 1.02 compared with -0.63 +/- 0.84 for length (P < 0.001 for both), respectively]. The percentage of infants with low ferritin values increased significantly between 6 and 12 mo of age in groups W, WF, and KF but not in group WM. Change in plasma retinol between 6 and 12 mo of age was significantly greater in group WM than in the other 3 groups combined (0.14 +/- 0.3 compared with -0.04 +/- 0.3 micromol/L, P = 0. 003).

CONCLUSIONS

All 4 foods improved growth relative to the NI group. Infants fed WM had better iron stores and vitamin A status than those fed nonfortified foods.

BACKGROUND

Accurate measurement of dietary intake is essential for understanding the long-term effects of adolescent diet on chronic disease risk. However, adolescents may have limited food knowledge and ability to quantify portion sizes and recall dietary intake. Therefore, food frequency questionnaires (FFQs) deemed appropriate for use among adults may not be suitable for adolescents.

OBJECTIVE

To evaluate an FFQ in comparison with a 3-day food record (FR) in 14-year olds participating in a population-based cohort study in Western Australia.

METHODS

Nutrient intakes estimated by a semi-quantitative FFQ were compared with those from a 3-day FR using Bland & Altman limits of agreement (LOA), tertile classifications and Pearson's correlation coefficients.

RESULTS

A total of 785 adolescents provided data from both dietary methods. Mean agreement between the FR and FFQ ranged from 73 (starch) to 161% (vitamin C). The LOA ranged from 27 (retinol) to 976% (carotene), with most nutrients being overestimated by the FFQ. For most nutrients, agreement between the two methods varied significantly with the magnitude of intake. Pearson's r ranged from 0.11 (polyunsaturated fats) to 0.52 (riboflavin). The FFQ classified 80 to 90% of subjects' nutrient intakes into the same or adjacent tertile as their FR. Boys performed slightly better for all of these indices.

CONCLUSIONS

Agreement between individual FFQ and FR nutrient intakes was less than ideal. However, the FFQ was able to correctly rank a reasonable proportion of adolescents.

OBJECTIVE

To describe a case of keratitis caused by the Gram-negative Escherichia coli, treated with UVA-riboflavin cross linking.

METHODS

Case report.

RESULTS

A 78-year-old woman with diabetes presented with a 1-week history of pain, photophobia, foreign body sensation, and lacrimation in the right eye. The patient underwent topical and systemic antimicrobial therapy, without improvement. The authors treated the patient with riboflavin and corneal UVA crosslinking, with the aim to promote healing of the ulceration. One day after the procedure, the corneal ulceration was covered by cicatricial tissue, and the patient reported a significant improvement in symptoms. One month after the treatment, corneal edema was almost completely resolved, corneal ulceration was healed, and the painful symptoms of the patient had disappeared.

CONCLUSIONS

UVA-riboflavin crosslinking can be useful for the treatment of corneal ulceration unresponsive to medical treatment.

Individuals with keratoconus form a significant proportion of patients for a practitioner specialising in corneal diseases. Yet it is a disease where the pathogenesis is poorly understood, and until recently, there has been no treatment apart from transplantation that could be offered that was curative or even capable of slowing the progression of the disease. Collagen cross-linking treatment using riboflavin and UV light has been developed to address this need, and the initial results are promising. The purpose of this review is to critically evaluate this treatment in light of the scientific basis for cross-linking, to highlight the strengths and limitations of the evidence in terms of efficacy and long-term safety, and finally to identify areas for future research in this area with a significant potential to change the way we treat our keratoconus patients. In addition, we hope that our unbiased review for the first time would bring together, in a concise fashion, scientific information for a practitioner contemplating on offering this treatment and to help inform their patients of its potential risks and benefits.

Riboflavin is a water-soluble vitamin (vitamin B2) required for the production of the flavin cofactors FMN and FAD. Mammals are unable to synthesize riboflavin and need a dietary supply of the vitamin. Riboflavin transport proteins operating in the plasma membrane thus have an important role in the absorption of the vitamin. However, their sequences remained elusive, and not a single eukaryotic riboflavin transporter is known to date. Here we used a genetic approach to isolate MCH5, a Saccharomyces cerevisiae gene with homology to mammalian monocarboxylate transporters, and characterize the protein as a plasma membrane transporter for riboflavin. This conclusion is based on the suppression of riboflavin biosynthetic mutants (rib mutants) by overexpression of MCH5 and by synthetic growth defects caused by deletion of MCH5 in rib mutants. We also show that cellular processes in multiple compartments are affected by deletion of MCH5 and localize the protein to the plasma membrane. Transport experiments in S. cerevisiae and Schizosaccharomyces pombe cells demonstrate that Mch5p is a high affinity transporter (Km = 17 microM) with a pH optimum at pH 7.5. Riboflavin uptake is not inhibited by protonophores, does not require metabolic energy, and operates by a facilitated diffusion mechanism. The expression of MCH5 is regulated by the cellular riboflavin content. This indicates that S. cerevisiae has a mechanism to sense riboflavin and avert riboflavin deficiency by increasing the expression of the plasma membrane transporter MCH5. Moreover, the other members of the MCH gene family appear to have unrelated functions.

The chemical and enzymatic properties of 26 analogues of riboflavin are presented. These analogues include both endo- and exocyclically substituted isoalloxazines with redox potentials from -370 to -128 mV. Physical and chemical data such as the electronic absorption spectra, pKas, and redox potentials of the analogues are presented and are discussed with respect to preferred tautomeric and resonance forms. Like riboflavin, most of the analogues are shown to be catalytic oxidants of dihydro-5-deazaflavins. Analogue binding to egg white binding apoprotein has been quantitated and serves to determine the origins of binding site specificity for this protein. Nearly all of the analogues that possess D-ribityl groups are found to be processed to the FAD level by the flavokinase/FAD synthetase system of Brevibacterium ammoniagenes. Most extensively studied are the reactivities of the analogues with the NAD(P)H:flavin oxidoreductase of Beneckea harveyi. Many of the analogues are substrates in this enzymatic redox reaction, and a linear free energy-rate relation (log Vmax vs. E0' of the analogue) is seen that parallels similar relationships in the nonenzymatic oxidation of dihydro-5-deazaflavins. This suggests a common mechanism for the reactions of such diverse flavins as riboflavin, 5-deazariboflavin, and 1-deazariboflavin.

OBJECTIVE

To determine the distribution of base damage within isolated DNA upon oxidation by three type I photosensitizers in aerated aqueous solution.

METHODS

Aqueous solutions of DNA were exposed to UVA in the presence of riboflavin, benzophenone or menadione. Then, eight modified nucleobases were measured, using HPLC-EC, GC-MS or HPLC with fluorescence detection.

RESULTS

The three photosensitizers led to a predominant degradation of guanine bases within DNA. The relative yield of the three main guanine degradation products measured in DNA was similar with the three sensitizers. 8-OxodAdo was also produced in an almost constant yield with respect to its guanine analogue. The yield of oxidized pyrimidines was lower and was found to depend on the photosensitizer used. The results were compared with the yield of photosensitization-induced degradation of the 2'-deoxyribonucleosides.

CONCLUSIONS

The favoured photosensitized degradation of guanine within DNA may be explained by its lower oxidation potential with respect to that of the other bases, together with the occurrence of charge transfer through DNA. The base modification pattern determined in the present work is different from that obtained upon reaction of hydroxyl radicals. Under the latter conditions, pyrimidine oxidation products were generated more efficiently than by photosensitized one-electron oxidation.

An enzyme that uses GTP as substrate for the formation in stoichiometric quantities of formate, inorganic pyrophosphate, and 2,5-diamino-6-hydroxy-4-(ribosylamino)pyrimidine-5'-phosphate has been purified 2200-fold from extracts of Escherichia coli B. This enzyme is named GTP cyclohydrolase II to distinguish it from a previously studied E. coli enzyme, named GTP cyclohydrolase (and called GTP cyclohydrolase I in this paper), that catalyzes the first of a series of enzymatic reactions leading to the biosynthesis of the pteridine portion of folic acid (Burg, A. W., and Brown, G. M. (1968) J. Biol. Chem. 243, 2349-2358). Some of the properties of GTP cyclohydrolase II are: (a) divalent cations are required for activity (Mg2+ is most effective); (b) its molecular weight, estimated by filtration on Sephadex G-200, is 44,000; (c) the K-m for GTP is 41 mum; (d) its pH optimum is 8.5; and (e) its activity is inhibited by inorganic pyrophosphate, one of the products of the reaction. Compounds not used as substrate are: GDP, GMP, guanosine, dGTP, ATP, ITP, and XTP. Properties a, b, c, and e (above), as well as the nature of the products, distinguish this enzyme from GTP cyclohydrolase I. Since GTP cyclohydrolase II apparently is not concerned with the biosynthesis of folic acid, the possible physiological role of this enzyme in the biosynthesis of riboflavin is considered in the light of the present investigations and the previously published work on riboflavin biosynthesis by other investigators.