The <em>17</em>beta-hydroxysteroid dehydrogenases (HSDs) are enzymes that catalyze the reduction of <em>17</em>-<em>ketosteroids</em> or the oxidation of <em>17</em>beta-hydroxysteroids. <em>17</em>beta-HSD type 12, the most recently cloned member of this gene family, was classified into the <em>17</em>beta-HSD family based on sequence homology, rather than steroid catalyzing activity. Meanwhile, it has been reported that <em>17</em>beta-HSD type 12 may be involved in fatty acid synthesis. To better understand the role of <em>17</em>beta-HSD type 12 in lipid metabolism, we determined the detailed systemic distribution and tissue localizations of <em>17</em>beta-HSD type 12, which, due partly to the lack of antibodies, had not yet been studied. We carried out these investigations by quantitative reverse transcription (RT)-PCR, Northern blot analysis, and immunohistochemistry, using an antibody against <em>17</em>beta-HSD type 12 that we have generated. <em>17</em>beta-HSD type 12 is highly expressed in organs related to lipid metabolism such as liver, kidney, heart and skeletal muscle. <em>17</em>beta-HSD type 12 is also detected in endocrine-related organs such as pancreas, pituitary gland, adrenal gland, testis and placenta, and in the gastrointestinal tract, which point to the possible involvement of <em>17</em>beta-HSD type 12 in the regulation of lipid biosynthesis and steroid metabolism. These results support previous reports and solidify the possibility that <em>17</em>beta-HSD type 12 may play critical roles in the physiological processes, such as fatty acid synthesis, in addition to the steroid metabolism.

A series of analogues of the neuroactive steroids 3 alpha-hydroxy-5 alpha-pregnan-20-one and 3 alpha-hydroxy-5 beta-pregnan-20-one were studied to elucidate the mode of binding of 5 alpha-and 5 beta-reduced steroids to steroid binding sites on GABAA receptors. Analogues which were either 3 alpha-hydroxy-20-<em>ketosteroids</em> or 3 alpha-hydroxysteroid-<em>17</em> beta-carbonitriles and which contained various methyl group substitution patterns at C-5 and C-10 were prepared. Evaluations utilized whole-cell patch clamp electrophysiological methods carried out on cultured rat hippocampal neurons, and the results obtained with the rigid <em>17</em> beta-carbonitrile analogs were analyzed using molecular modeling methods. The molecular modeling results provide a rationale for the observation that the configuration of the hydroxyl group at C-3 is a greater determinant of anesthetic potency than the configuration of the A,B ring fusion at C-5. The electrophysiological results identify steric restrictions for the space that can be occupied in 5 alpha- and 5 beta-reduced steroid modulators of GABAA receptors in the regions of space proximate to the steroid C-5, C-10, and possibly C-4 positions. This information is useful for the development of nonsteroidal analogues that can modulate GABAA receptors via interactions at steroid binding sites.

We describe a middle-aged man with late-onset multiple sclerosis and an incidentally discovered asymptomatic adrenal mass. He had no symptoms or signs of hypercortisolism. A 24-h profile revealed fluctuating serum cortisol values (between 15.1 and 4.7 micrograms/dl) and inappropriately low plasma ACTH values. Urinary cortisol excretion was 89 and 106 micrograms/day on two occasions. After a 4-h ACTH infusion, serum cortisol rose from 6.3 to 108 micrograms/dl. The serum dehydroepiandrosterone level, 33 ng/dl before ACTH stimulation, did not change. During dexamethasone administration, the lowest daily urinary cortisol excretion was 37 micrograms/day, and <em>17</em>-<em>ketosteroid</em> excretion was 8 mg/day. The response to metyrapone showed a rise of serum 11-deoxycortisol to 25.6 micrograms/dl and of ACTH to 169.5 pg/ml. After removal of the tumor, most likely an adenoma, the circadian pattern of cortisol and ACTH was normal. During a 4-h ACTH infusion, the serum cortisol level rose from 10 to 27 micrograms/dl, and dehydroepiandrosterone rose from 62 to 90 ng/dl. During dexamethasone administration, daily urinary cortisol excretion decreased to 12 micrograms/day, and <em>17</em>-<em>ketosteroid</em> excretion dropped to 3.9 mg/day. These data show that while the tumor appeared clinically to be nonfunctional, it was producing cortisol and possibly androgens autonomously, albeit at levels too low to cause complete suppression of the pituitary-adrenal axis.

Complete endocrinologic evaluation of 9 women (ages 24-41) with idiopathic melasma (melasma not associated with pregnancy nor ingestion of oral contraceptives) was performed and compared to age- and sex-matched normal controls. Serum cortisol, adrenocorticotropin, plasma immunoreactive alpha and beta melanocyte-stimulating hormones, luteinizing hormone, follicular-stimulating hormone, estradiol and progesterone levels were performed in the basal state. Additionally, total T4, T3RU, FTI, prolactin, 2-h postprandial blood sugar, and 24-h urine for <em>17</em>-hydroxysteroids and <em>17</em>-<em>ketosteroids</em> were done and found to be normal. The melasma patients presented statistically significant increased levels of LH (p less than 0.001) and lower levels of serum estradiol (p less than 0.025) than normal controls. It is proposed that these hormonal alterations may represent subclinical evidence of a mild ovarian dysfunction which may underlie the pathogenesis of some cases of idiopathic melasma.

We have shown by kinetic and magnetic resonance measurements that a spin-labeled substrate analogue, spiro[doxyl-2,3'-5' alpha-androstan]-<em>17</em>'beta-ol, binds at the substrate site of crystalline delta 5-3-<em>ketosteroid</em> isomerase (steroid delta-isomerase; EC 5.3.3.1) of Pseudomonas testosteroni. The spin-labeled steroid is a linear competitive inhibitor with a Ki value (25 +/- 5 microM) that is consistent with dissociation constants obtained by direct binding measurements based on changes in the electron paramagnetic resonance spectrum of the nitroxide, longitudinal relaxation rates of water protons, and longitudinal and transverse relaxation rates of carbon-bound protons of the isomerase. These binding studies yield a stoichiometry for the nitroxide of 1 per subunit of the enzyme. Measurements of the longitudinal relaxation rates of water protons indicate that the 3-doxyl portion of the spin-label is highly immobilized yet is exposed to solvent. Paramagnetic effects of the nitroxide on T1 defined distances to several previously assigned [Benisek, W. F., & Ogez, J. R. (1982) Biochemistry 21, 5816-5825] and newly assigned protons of the enzyme. These distances were then used to locate (with an accuracy of +/- 2 A) the nitroxide moiety at a unique position in a partially refined 2.5-A resolution X-ray structure of native isomerase. Three of five additional proton resonance peaks, attributed to ring-shielded methyl groups, could be assigned to specific residues on the basis of distances from the spin-label in the X-ray structure. The remaining portion of the spin-labeled steroid was then docked into the X-ray structure in a hydrophobic cavity of the enzyme. This position of the steroid is consistent with the steroid binding site previously proposed [Westbrook, E. M., Piro, O. E., & Sigler, P. B. (1984) J. Biol. Chem. 259, 9096-9103]. However, the rotational orientation of this steroid about its long axis could not be unambiguously established. If we assume that steroid substrates and the spin-labeled inhibitor bind to the same site, but with reversal of the 3- and <em>17</em>-positions, then the phenolic hydroxyl of Tyr-55 is optimally positioned to function as the general acid that protonates the 3-keto group of the substrate, facilitated by the negative end of the dipole of a 10-residue alpha-helix, the only helix in the molecule.(ABSTRACT TRUNCATED AT 400 WORDS)

The aim of this study was to determine whether definite diet changes affect adrenocortical activity and/or adrenal androgen metabolism. A controlled experimental diet study with four consecutive diet periods (repeated measure design) was carried out in six healthy adult volunteers. Four nearly isoenergetic diets, two normal (N) moderately protein-rich, one protein-rich (P), and one low protein lactovegetarian (L), were fed. At the end of each 5-day diet period a blood sample and two 24-h urine specimens were obtained from each subject. Plasma levels of dehydroepiandrosterone sulfate (DHEAS) were elevated with diet L (6.5 +/- 1.4 vs. 5.3 +/- 1.1 mumol/L; P < 0.05) compared to diet N, whereas other plasma hormones, including cortisol and insulin-like growth factor I did not vary markedly. A marked increase of 60% was seen in the urinary 24-h output of 3 alpha-androstanediol glucuronide with diet P. Urinary 24-h excretion rates for C peptide, free cortisol, DHEAS, and total <em>17</em>-<em>ketosteroid</em> sulfates were clearly reduced with diet L compared to those with diet N or P. Our results show that a lactovegetarian diet can reduce adrenocortical activity (at least after a short term diet change). In addition, this vegetarian nutrition leads to a particular metabolic situation (elevated plasma DHEAS and reduced urinary DHEAS output) that usually is characteristic of fasting. Peripheral androgen metabolism as reflected by urinary 3 alpha-androstanediol glucuronide appears to be influenced only by high protein intake (diet P). Further research (controlled dietary long term investigation) is required 1) to validate whether the effects of diet on adrenocortical activity represent sustained endocrine changes and 2) to elucidate the underlying mechanism.

Two sisters (28 and 30 years) were investigated for primary infertility and milk hirsutism. Both had normal puberty, were having regular menses and had normal female sexual characteristics. Studies revealed elevated urinary <em>17</em>-<em>ketosteroid</em> levels (15.8, 18.8 mg/24 hours) and increased serum levels of <em>17</em>-OH-progesterone (2,756, 1,121 ng/dl), 21-desoxycortisol (1,882, 1,090 ng/dl), progesterone (300, 346 ng/dl), dehydroepiandrosterone (DHA) (1,600, 1,700 ng/dl), and androstenedione (402, 366 ng/dl) and testosterone (100, 104 ng/dl), together with a slight increase in serum 11-desoxycortisol (1,180, 1,560 ng/dl). Blood pressure, serum sodium/potassium plasma renin and serum aldosterone, corticosterone, 11-desoxycorticosterone and cortisol levels were normal. The administration of ACTH caused a further increase in 21-hydroxylase precursors; the administration of dexamethasone normalized hormone levels and produced ovulatory cycles. Similar studies in two siblings were normal. The affected sisters were HLA identical and did not share any HLA antigens with their healthy siblings. The data suggest that these patients have a mild form of 21-hydroxylase deficiency which was insufficient to cause prenatal virilization. The gene for this disorder may be allelic with that for typical congenital adrenal hyperplasia.

OBJECTIVE

To characterize aldo-keto reductase 1C3 (AKR1C3) expression in surgically-removed cryptorchid testes. Human AKR1C3 is a monomeric, cytoplasmic, multifunctional enzyme that reduces ketosteroids, ketoprostaglandins, and lipid aldehydes. AKR1C3 expression has been demonstrated in normal adult Leydig cells and peritubular fibromyocytes. No prior studies have evaluated AKR1C3 expression patterns across different age groups.

METHODS

Surgically excised cryptorchid testes were subjected to hematoxylin-eosin evaluation to review overall testicular pathology. These samples were then evaluated for AKR1C3 distribution via immunohistochemical staining with a monospecific AKR1C3 monoclonal antibody. Single-pathologist grading of AKR1C3 expression was correlated with clinical presentations.

RESULTS

A total of 16 cryptorchid testes were identified from the 2000 to present. Median age at the time of surgery was 9 years (range, 1-17). The testes were excised due to atrophy, poor tissue consistency, and short spermatic cord length. AKR1C3 expression was identified at all ages in fibromyocytes surrounding the testicular tubules. Leydig cell expression was absent at Tanner stages 1 and 2, while strong expression was found at Tanner stage 3 and beyond. No AKR1C3 expression was seen in germ cells at any stage. AKR1C3 expression was identified in 18%-26% of Sertoli cells in patients at Tanner stages 2 and beyond.

CONCLUSIONS

AKR1C3 expression occurs in a Tanner stage dependent-fashion. Pre- and peri-pubertal changes appear to promote expression of the enzyme in Leydig cells. In contrast to the normal adult testis, the pediatric cryptorchid testis reveals AKR1C3 expression in Sertoli cells. Additional studies are warranted to determine the involvement of AKR1C3 in testicular descent and development.

The subcellular distribution and properties of rat hypothalamic progesterone 5 alpha-reductase, which accelerates the conversion of progesterone to 5 alpha-pregnane-3,20-dione, have been investigated by utilizing 3H-labeled substrate and a reverse isotopic dilution assay system. The enxymic activity was associated primarily with a cell debris-membranes fraction deribed from the 100 x g pellet. This fraction contained mainly membrane-like particulates and was free of nuclei. Little or no activity was associated with the purified nuclei. The hypothalamic 5 alpha-reductase was stimulated by NADPH but not by NADH. The reaction proceeded optimally over a pH range of 6.0 to 7.2 and at a temperaturhe substrate specificity of the enzyme for other delta 4-3-<em>ketosteroids</em> and the ability of these steroids to inhibit the 5 alpha reduction of [1,2-3H]progesterone as well as the effect of <em>17</em> beta-estradiol were also studied. 20 alpha-hydroxypregn-4-en-3-one was more reactive that progesterone, while testosterone was the least reactive. The estimated Km for 20 alpha-hydroxypregn-4-en-3-one was 8.6 +/- 1.9 x 10(-7) M, and for testosterone, 1.6 +/- 1.4 x 10(-5) M. The inhibition studies indicate that 20 alpha-hydroxypregn-4-en-3-one and <em>17</em> beta-estradiol are competitive and noncompetitive inhibitors, respectively, of the 5 alpha reduction of progesterone with Ki of 6.0 +/- 3.0 x 10(-8) M for 20 alpha-hydroxypregn-4-en-3-one and Kii (intercept inhibition constant) of 2.6 +/- 0.7 x 10(-5) M and Kis (slope inhibition constant) of 3.6 +/- 0.6 x 10(-5) M for <em>17</em> beta-estradiol. Testosterone is a poor competitive inhibitor of the reaction.

Seventeen patients with adrenal adenoma causing Cushing's syndrome, eight patients with Cushing's disease due to hypersecretion of ACTH, and five patients with primary aldosteronism due to an aldosteronoma were studied for their computed tomographic (CT) patterns, hormonal profiles, and macroscopic and microscopic findings of the adrenal gland. Black (or brown) adrenal adenomas were found in 71% of the patients with Cushing's syndrome, but not in patients with aldosteronoma. The adrenal tissue of patients with Cushing's disease was predominantly yellow. The number of compact cells was larger in black or brown adenomas than in yellow tumors or hyperplastic adrenal tissue. In patients with Cushing's syndrome, urinary excretion of <em>17</em>-<em>ketosteroids</em> (<em>17</em>-KS) and serum aldosterone concentrations were lower in those with black or brown adenomas than in those with yellow adenomas (P less than 0.05). Patients with Cushing's disease had even higher <em>17</em>-KS and serum aldosterone levels. No difference was found in serum cortisol concentrations and dexamethasone suppressibility in two types of adenomas causing Cushing's syndrome. Visual estimation of radiological density of the adrenal tissue relative to the kidney on CT scan and quantitative measurement of it by CT number revealed a difference between the two types of adrenal tumors causing Cushing's syndrome. Adrenal tumors with decreased density on CT scan were yellow adenomas with predominantly clear cells, and those with equal or increased density were black or brown adenomas with predominantly compact cells. All aldosteronomas had decreased density and consisted of clear cells. It is suggested that black or brown adenomas of the adrenal gland have higher radiological density and accompanying lower serum aldosterone and urinary <em>17</em>-KS levels than ordinary yellow tumors. The abundance of compact cells may have some significance for the development of this particular type of adrenal tumor.

A 36-year-old white patient is described. He received treatment for hypertension and showed slightly increased excretion of <em>17</em>-OHCS- and <em>17</em>-<em>ketosteroids</em> but no increase in values for 3-methoxy-4-hydroxymandelic acid in the urine. He was admitted to hospital for a myocardial infarction, which was found to be situated in the anterior wall. During his stay in hospital a sudden increase in blood pressure occurred, together with a typical attach of perspiration, loss of consciousness, and ventricular fibrillation. The assay by 3-methoxy-4-hydroxymandelic acid now showed markedly increased amounts. A phaeochromocytoma was thought to be the most probably diagnosis, but now withstanding therapy the patient died from cerebral lesions. At necropsy a recent anteroseptal myocardial infarction and some minor lesions were found but no tumour and notably no phaechromocytoma, neither in the adrenals nor elsewhere. Using Dobbie's morphometric technique, as described by Munro Neville (1969), changes in the adrenals were demonstrated, which were considered to represent primary adrenal medullary hyperplasia. Criteria for the diagnosis of this syndrome are discussed. Until now it had been presumed to be present in a number of cases but never convincingly demonstrated.

Six patients with congenital virilizing adrenal hyperplasia were evaluated on single- and multiple-dose prednisone schedules. Each of the treatment periods was for one month. Patients were evaluated by 24-hour urinary excretion of <em>17</em>-<em>ketosteroids</em> and pregnanetriol, as well as 0900 plasma concentrations of <em>17</em>-hydroxyprogesterone, progesterone, and testosterone. By the criteria of urinary excretion of KS and PNT appropriate for chronologic age, three of the six patients were adequately controlled on prednisone given once a day. Prednisone administered twice daily at 12-hourly intervals either in equally divided doses or with a larger dose in the evening, however, resulted in adequate suppression in all patients. Because of the marked diurnal variation of plasma <em>17</em>-OHP, the time of day that the sample is drawn is critical. Afternoon samples are often misleadingly low. Plasma <em>17</em>-OHP concentration may reflect escape from therapeutic control sooner than urinary KS and PNT excretion. There was no correlation between <em>17</em>-OHP and P values. Plasma concentration of T was not a reliable indicator of good control, since T values were often at prepubertal levels when urinary KS and PNT were elevated.

A patient with virilization was studied. The basal urinary excretion of <em>17</em>-<em>ketosteroids</em> was at the upper limit of normal, but the plasma testosterone concentration was greatly elevated. Testosterone secretion could be stimulated by hCG, suppressed by dexamethasone, and was not affected by ACTH. At operation, an arrhenoblastoma of the left ovary was found. Isolated tumor cells in culture secreted testosterone. The addition of a LRH agonist (10 ng/ml) suppressed the secretion of testosterone by 50% (P less than 0.01). The inhibiting effect of a LRH agonist on steroidogenesis suggests that LRH receptors were present on this tumor and that treatment with LRH agonists might be beneficial in patients with metastatic steroid hormone-secreting ovarian and testicular tumors.

We found elevations of plasma dehydroepiandrosterone-sulfate (DHAS) in five boys, 5.5 to 10.3 years of age (group A), with premature pubarche (pubic hair development) or acne as an isolated phenomenon. Four boys (group B) with seemingly idiopathic premature pubarche (DHAS normal for age) were discovered to have above-average dehydroepiandrosterone levels. All of these boys with premature pubarche had some evidence of cerebral dysfunction or were obese. Plasma testosterone values and bone age were not markedly increased in either group. In each case studied, the patterns of plasma steroid intermediates before and after administration of adenocorticotropin were typical of adrenarche rather than of congenital adrenal hyperplasia or Cushing syndrome. In addition, DHAS was dexamethasone suppressible, and in those patients in whom nocturnal testosterone sampling or gonadotropin-releasing hormone testing was performed, no evidence of true puberty could be found. Fifteen percent of our normal male volunteers over 10 years of age developed pubarche with plasma DHAS levels over 120 micrograms/dl without evidence of true puberty. Thus pubarche as an isolated phenomenon does not necessarily indicate a virilizing disorder or true puberty. In the majority of cases, isolated pubarche appears to be the result of isolated adrenarche, the maturational increase in adrenal production of <em>17</em>-<em>ketosteroids</em>.

BACKGROUND

Dehydroepiandrosterone (DHEA), an adrenal <em>17</em>-<em>ketosteroid</em>, is a precursor of testosterone and <em>17</em>beta-estradiol. Studies have shown that DHEA inhibits carcinogenesis in mammary gland and prostate as well as other organs, a process that is not hormone dependent. Little is known about the molecular mechanisms of DHEA-mediated inhibition of the neoplastic process. Here we examine whether DHEA and its analog DHEA 8354 can suppress the progression of hyperplastic and premalignant (carcinoma in situ) lesions in mammary gland toward malignant tumors and the cellular mechanisms involved.

METHODS

Rats were treated with N-nitroso-N-methylurea and allowed to develop mammary hyperplastic and premalignant lesions with a maximum frequency 6 weeks after carcinogen administration. The animals were then given DHEA or DHEA 8354 in the diet at 125 or 1,000 mg/kg diet for 6 weeks. The effect of these agents on induction of apoptosis, senescence, cell proliferation, tumor burden and various effectors of cellular signaling were determined.

RESULTS

Both agents induced a dose-dependent decrease in tumor multiplicity and in tumor burden. In addition they induced a senescent phenotype in tumor cells, inhibited cell proliferation and increased the number of apoptotic cells. The DHEA-induced cellular effects were associated with increased expression of p16 and p21, but not p53 expression, implicating a p53-independent mechanism in their action.

CONCLUSIONS

We provide evidence that DHEA and DHEA 8354 can suppress mammary carcinogenesis by altering various cellular functions, inducing cellular senescence, in tumor cells with the potential involvement of p16 and p21 in mediating these effects.

The endocrine effects of ketoconazole (400 mg orally every 8 h) were studied in 9 previously untreated patients with advanced prostatic cancer. Five of these patients were followed for 12 months. A rapid fall in the serum concentration of testosterone was noted in all patients studied. Minimal values were observed on day 4 of treatment but thereafter serum testosterone increased slowly. The effect of the drug on unbound testosterone was relatively more important, since sex hormone binding globulin increased markedly during treatment. An increase in progesterone and LH was observed in all patients. This suggests that ketoconazole limits the conversion of C21-precursors into androgens. This block is compensated in part by activation of the hypothalamo-hypophyseal feedback system. Urinary <em>17</em>-<em>ketosteroids</em> were decreased but <em>17</em>-hydroxysteroids were unaffected by the treatment. In 5 patients followed monthly over a period of 12 months the mean testosterone concentration ranged from 69 ng/100 ml in one patient to 428 ng/100 ml in another. An excellent inverse correlation could be demonstrated between the mean serum concentration of testosterone and the mean concentration of ketoconazole. The change of serum dehydroepiandrosterone sulphate also correlated inversely with the mean ketoconazole level. Increased concentrations of oestradiol were noted in 2 patients with slight gynaecomastia. It is concluded that long-term suppression of androgen production can be realized by high-dose ketoconazole treatment and that the degree of suppression is proportional to the serum levels of the drug.

The spectrum of biological rhythms is extended far beyond circadians, circannuals, and ultradians, such as 1.5-hourly melatonin and 8-hourly endothelin-1 (ET-1) rhythms by statistics of natality, growth, morbidity, and mortality, some covering decades or centuries on millions of individuals. These reveal infradian cycles to be aligned with half-weekly rhythms in ET-1, weekly and half-yearly ones in melatonin, and even longer--about 50-, about 20-, and about 10-year cycles found in birth statistics. About daily, weekly, yearly, and ten-yearly patterns are also found in mortality from myocardial infarctions; the 10-yearly ones are also in heart rate and its variability; in steroid excretion, an aspect of resistance, for example, to bacteria; and in the genetic changes of the bacteria themselves. Automatic physiological measurements cover years and, in one case, cover a decade; the latter reveal an about 10-year (circadecennial) cycle. ECGs, covering months beat-to-beat, reveal circaseptans, gaining prominence in response to magnetic storms or after coronary artery bypass grafting. A spectrum including cycles from fractions of 1 Hz to circasemicentennians is just one element in biological time structures, chronomes. Chaos, trends, and any unresolved variability are the second to fourth elements of chronomes. Intermodulations, feedsidewards, account for rhythmically and thus predictably recurring quantitive differences and even for opposite treatment effects of the same total dose(s) of (1) immunomodulators inhibiting or stimulating DNA labeling of bone in health or speeding up versus slowing down a malignant growth and thus shortening or lengthening survival time, or (2) raising or lowering blood pressure or heart rate in the vascular aspect of the body's defense. Latitude-dependent competing photic and nonphotic solar effects upon the pineal are gauged by alternating yearly (by daylight) and half-yearly (by night) signatures of circulating melatonin at middle latitudes and by half-yearly signatures at noon near the pole. These many (including novel near 10-yearly) changes, for example, in <em>17</em>-<em>ketosteroid</em> excretion, heart rate, heart rate variability, and myocardial infarction in us and those galactic, solar, and geophysical ones around us have their own special signatures and contribute to a cosmo-vasculo-immunity and, if that fails, to a cosmo(immuno?) pathology.

The chemical change responsible for the 3-oxo-4-estren-<em>17</em> beta-yl acetate-dependent photoinactivation of delta 5-3-<em>ketosteroid</em> isomerase has been identified by amino acid analysis and amino acid sequencing. Amino acid analysis of the enzyme and its photoinactivated derivative shows that photoinactivation is accompanied by loss of nearly 1 residue of aspartic acid/polypeptide chain and an increase in nearly 1 residue of alanine. Edman degradation of a peptide comprising residues 31 to 48 from native isomerase showed the presence of aspartic acid at residue 38. When the corresponding peptide from photoinactivated enzyme was sequenced, residue 38 was revealed to be alanine.

Two NADPH-dependent aromatic aldehyde-ketone reductases purified from guinea pig liver catalyzed oxidoreduction of <em>17</em> beta-hydroxysteroids and <em>17</em>-<em>ketosteroids</em>. One enzyme efficiently oxidized 5 beta-androstanes and reduced <em>17</em>-<em>ketosteroids</em> of A/B cis configuration, whereas the other enzyme efficiently oxidized 5 alpha-androstanes and equally reduced both 5 alpha-and 5 beta-androstanes of <em>17</em>-<em>ketosteroids</em>. However, aromatic aldehydes and ketones, and 3-<em>ketosteroids</em> were irreversibly reduced by the two enzymes. The two enzymes utilized NADP+ or NADPH as cofactor, but little activity with NAD+ or NADH was found. Phosphate ions enhanced the NAD+-dependent dehydrogenase activity and NADH-dependent reductase activity of the two enzymes, whereas the activities with NADP+ and NADPH were not affected. The ratios of the two activities of ketone reduction and <em>17</em> beta-hydroxysteroid oxidation of the two enzymes were almost constant during the purification steps after the two enzymes had been separated by DEAE-cellulose chromatography. By kinetic studies and electrophoresis and isoelectric focusing experiments it was confirmed that both of the two enzymes were responsile for the reduction aldehydes, ketones, and <em>ketosteroids</em> and for the oxidation of <em>17</em> beta-hydroxysteroids. These results indicate that <em>17</em> beta-hydroxysteroid dehydrogenases may play important roles in the metabolism of exogeneous aldehydes and ketones as well as steroids.