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Papers by Robert Morfin

Cytochrome P4507B1 7␣-hydroxylates dehydroepiandrosterone (DHEA), epiandrosterone (EpiA) and 5␣an... more Cytochrome P4507B1 7␣-hydroxylates dehydroepiandrosterone (DHEA), epiandrosterone (EpiA) and 5␣androstane-3␤,17␤-diol (Adiol). 11␤-Hydroxysteroid dehydrogenase type 1 (11␤-HSD1) interconverts 7␣-and 7␤-forms. Whether the interconversion proceeds through oxido-reductive steps or epimerase activity was investigated. Experiments using [ 3 H]-labelled 7␤-hydroxy-DHEA, 7␤-hydroxy-EpiA and 7␤hydroxy-Adiol showed the 3 H-label to accumulate in the 7-oxo-DHEA trap but not in 7-oxo-EpiA or 7-oxo-Adiol traps. Computed models of 7-oxygenated steroids docked in the active site of 11␤-HSD1 either in a flipped or turned form relative to cortisone and cortisol. 7-Oxo-steroid reduction in 7␣-o r 7␤-hydroxylated derivatives resulted from either turned or flipped forms. 11␤-HSD1 incubation in H 2 18 O medium with each 7-hydroxysteroid did not incorporate 18 O in 7-hydroxylated derivatives of EpiA and Adiol independently of the cofactor used. Thus oxido-reductive steps apply for the interconversion of 7␣and 7␤-hydroxy-DHEA through 7-oxo-DHEA. Epimerization may proceed on the 7-hydroxylated derivatives of EpiA and Adiol through a mechanism involving the cofactor and Ser 170 . The physiopathological importance of this epimerization process is related to 7␤-hydroxy-EpiA production and its effects in triggering the resolution of inflammation.

Life Sci, 1998

Dehydroepiandrosterone (DHEA) is 7α-hydroxylated in liver, brain and other organs of murine and i... more Dehydroepiandrosterone (DHEA) is 7α-hydroxylated in liver, brain and other organs of murine and in other species. Several works suggest that the 7α-hydroxy-DHEA produced may be one of the native antiglucocorticoids, and compounds modifying its production may prove useful in investigation of 7α-hydroxy-DHEA production and effects. After treatment of mice with dexamethasone, phenobarbital, trilostane, melatonin or metyrapone,. we have used gas chromatography-mass spectrometry with negative ion detection for measurement of 7α-hydroxy-DHEA levels in serum of control and treated animals. The 7α-hydroxylating rates of liver and brain microsomes from the same animals were also measured. Results showed that serum levels of 7α-hydroxy-DHEA were significantly increased after treatment by all compounds except metyrapone. Significantly increased 7α-hydroxy-DHEA levels were directly related with significantly increased 7α-hydroxylation yields in liver and not in brain. In contrast, metyrapone decreased 7α-hydroxylation in liver and brain. These findings indicate that in brain and in liver, different enzyme systems may be responsible for production of 7α-hydroxy-DHEA and that treatment-induced modifications of circulating 7α-hydroxy-DHEA levels are mainly due to change of 7α-hydroxylating rates in liver.

European journal of biochemistry / FEBS, 1981

The present study applied high-pressure liquid chromatography, gas chromatography/mass spectromet... more The present study applied high-pressure liquid chromatography, gas chromatography/mass spectrometry and crystallizations to constant specific activity for identification of the radiometabolites of tritiated zearalenone and alpha-zearalanol in homogenates of human prostate glands. Radiolabelled zearalenone or alpha-zearalanol (6.3 microM) was incubated for 30 min at 37 degrees C with prostatic homogenate in 5 ml 0.067 M phosphate buffer (pH 7.4) containing 0.5 mM oxidized or reduced NAD or NADP. Reduction of zearalenone occurred only with NADPH while oxidation of alpha-zearalanol was favoured both by NADP+ and NAD+. Separation of the substrates from their metabolites by high-pressure liquid chromatography showed the radioactivity of the metabolite of zearalenone to be associated with the alpha-zearalenol carrier while that of the alpha-zearalanol metabolite was found with the zearalanone carrier. Crystallizations to constant specific activity after isotopic dilution and gas chromatog...

Steroids, 2008

This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.

Steroids, 1985

The metabolism of testosterone in the uropygial gland of the quail principally results in the pro... more The metabolism of testosterone in the uropygial gland of the quail principally results in the production of 17α, 5β derivatives. Moreover, an unusually small amount of testosterone is converted to 5αdihydrotestosterone. These results question the role played by intracellular 5α-reduction in the response of the gland to testosterone stimulation.

Steroids, 1996

Hydroxylation of pregnenolone (PREG) and dehydroepiandrosterone (DHEA) is known ta take place in ... more Hydroxylation of pregnenolone (PREG) and dehydroepiandrosterone (DHEA) is known ta take place in numerous tissues ofmouse and rat. The responsible cytochrome P450 species has nO( yet been identified. Interest in the production of 7a.-hydroxylated steroid derivatives results from their abiliry ta increase the immune response in mice. Using crystallizations to constant specific activity and gas chromatography-mass spectrometry, 7a-hydroxy-PREG and 7a.-hydroxy-DHEA metabolites produced by microsomes of liver, brain, thymus, and spleen were identified. Study ofthe 7a.-hydroxylating enzyme in these tissues indicated tOOt microsomes contained most of the activity, except for brain, where it was primarily mitachondrial. Production yieids of 7a-hydroxy-PREG and 7a-hydroxy-DHEA by microsomes from heart, spleen, thymus, brain, and liver of 7-week-old mice were higher than those of I-week-old and (exceptfor liver) 41-week-old animais. At the optimal pH (7.4) and in ail tested tissues but liver. microsomai 7a-hydroxyiation was more extensive for PREG than for DHEA. With brain and thymus microsomes. KM were iower for PREG tlum for DHEA and decreased when phosphate was used instead of Tris buffer. With brain microsomes. the use of 1 mM EDTA increased 7a-hydroxylating activity. Complete inhibition was obtained with 0.1 mM Zn 2 + or Cu 2 + and with 1 mM Fe 2 + or Fe 3 +. 7a-HydrOJ"ylation of PREG was activated ont y by 0.5 mM Ca 2 + and that of DHEA only by 0.25 mM Mg 2 +. Since the production rates of 7a-hydroxy-PREG and 7a-hydroxy-DHEA in tissues ma}' be a key 10 the triggering of immune defenses, alld since both 7a-hydroxylation and immunity decrease with aging, these data will prove to be usefut in studies of the enzyme responsible and of the mechanisms that control its activit)'. Address reprint requests to Prof. R. Morfin. Biotechnologie. CNAM. 2 rue be based on a sound knowledge of ils properties. To locate Conté, 75141 PARIS Cedex 03. France.

Nature Precedings, 2008

Cytochrome P4507B1 7α α α α-hydroxylates dehydroepiandrosterone (DHEA), epiandrosterone (EpiA) an... more Cytochrome P4507B1 7α α α α-hydroxylates dehydroepiandrosterone (DHEA), epiandrosterone (EpiA) and 5α α α α-androstane-3β β β β,17β β β β-diol (Adiol). 11β β β β-Hydroxysteroid dehydrogenase type 1 (11β β β β-HSD1) interconverts 7α α α αand 7β β β βforms. Whether the interconversion proceeds through oxido-reductive steps or epimerase activity is investigated.

Life Sciences, 1998

The Prostate, 2007

BACKGROUND. Cytochrome P450 (CYP) 7B1 is involved in many metabolic processes including androgen ... more BACKGROUND. Cytochrome P450 (CYP) 7B1 is involved in many metabolic processes including androgen metabolism. Cytochrome P450 (CYP) 7B1 is expressed within the prostate and may determine the levels of the natural estrogen receptor b (ERb) ligand 5a-androstane-3b,17b-diol (3bAdiol) available and hence affect the regulation of prostate proliferation. We hypothesized that CYP7B1 expression is increased in prostate tumors and that promoter methylation contributes to the regulation of CYP7B1 expression in human prostate tissue. METHODS. Expression of the CYP7B1 gene and protein in clinical prostate tissues and prostate cancer cell lines were investigated using real-time PCR and immunohistochemistry. The methylation status of the CYP7B1 gene was analyzed using methylation-specific PCR (MSP). RESULTS. The immunohistochemical results demonstrate that high expression of CYP7B1 protein occurs in high-grade prostatic intraepithelial neoplasia (PIN) and adenocarcinomas. The ERb/CYP7B1 mRNA ratio was significantly lower in tumor compared to the non-tumor area. The MSP analysis indicate that local methylation of CYP7B1 promoter region is an important mechanism involved in down-regulation of CYP7B1 in human prostate tissue. CONCLUSIONS. This is the first report showing that CYP7B1 is overexpressed in high-grade PIN and in prostate cancer and that local methylation of CYP7B1 promoter region may have significant effect on gene transcription.

The Journal of Steroid Biochemistry and Molecular Biology, 2006

Circulating 3beta-hydroxysteroids including dehydroepiandrosterone (DHEA) are 7alpha-hydroxylated... more Circulating 3beta-hydroxysteroids including dehydroepiandrosterone (DHEA) are 7alpha-hydroxylated by the cytochrome P450-7B1 in the liver, skin and brain, which are the target organs of glucocorticoids. Anti-glucocorticoid effects with 7alpha-hydroxy-DHEA were observed in vivo without an interference with glucocorticoid binding to its receptor. In the organs mentioned above, the circulating inactive cortisone was reduced into active cortisol by the 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1). We demonstrated that 7alpha-hydroxy-DHEA was also a substrate for this enzyme. Studies of the 11beta-HSD1 action on 7alpha-hydroxy-DHEA showed the reversible production of 7beta-hydroxy-DHEA through an intermediary 7-oxo-DHEA, and the kinetic parameters favored this production over that of active glucocorticoids. Both the production of 7alpha-hydroxysteroids and their interference with the activation of cortisone into cortisol are basic to the concept of native anti-glucocorticoids efficient at their production site. This opens a promising new area for research.

The Journal of Steroid Biochemistry and Molecular Biology, 2006

The dehydroepiandrosterone (DHEA) 7␣-hydroxylation in humans takes place in the liver, skin, and ... more The dehydroepiandrosterone (DHEA) 7␣-hydroxylation in humans takes place in the liver, skin, and brain. These organs are targets for the glucocorticoid hormones where 11␤-hydroxysteroid dehydrogenase type 1 (11␤-HSD1) activates cortisone through its reduction into cortisol. The putative interference of 7␣-hydroxy-DHEA with the 11␤-HSD1-catalyzed reduction of cortisone into cortisol has been confirmed in preliminary works with human liver tissue preparations of the enzyme demonstrating the transformation of 7␣-hydroxy-DHEA into 7-oxo-DHEA and 7␤-hydroxy-DHEA. However, the large production of 7␤-hydroxy-DHEA could not be explained satisfactorily. Therefore our objective was to study the role in the metabolism of oxygenated DHEA by recombinant human 11␤-HSD1 expressed in yeast. The 7␣-and 7␤-hydroxy-DHEA were each oxidized into 7-oxo-DHEA with quite dissimilar K M (70 and 9.5 M, respectively) but at equivalent V max .In contrast, the 11␤-HSD1-mediated reduction of 7-oxo-DHEA led to the production of both 7␣-and 7␤-hydroxy-DHEA with equivalent K M (1.1 M) but with a 7␤-hydroxy-DHEA production characterized by a significantly greater V max . The 7␣-hydroxy-DHEA produced by the cytochrome CYP7B1 in tissues may exert anti-glucocorticoid effects through interference with the 11␤-HSD1-mediated cortisone reduction.

The Journal of Steroid Biochemistry and Molecular Biology, 2007

Dehydroepiandrosterone (DHEA) is 7␣-hydroxylated by the cytochome P450 7B1 (CYP7B1) in the human ... more Dehydroepiandrosterone (DHEA) is 7␣-hydroxylated by the cytochome P450 7B1 (CYP7B1) in the human brain and liver. This produces 7␣-hydroxy-DHEA that is a substrate for 11␤-hydroxysteroid dehydrogenase type 1 (11␤-HSD1) which exists in the same tissues and carries out the inter-conversion of 7␣-and 7␤-hydroxy-DHEA through a 7-oxo-intermediary. Since the role of 11␤-HSD1 is to transform the inactive cortisone into active cortisol, its competitive inhibition by 7␣-hydroxy-DHEA may support the paradigm of native anti-glucocorticoid arising from DHEA. Therefore, our objective was to use human tissues to assess the presences of both CYP7B1 and 11␤-HSD1. Human skin was selected then and used to test its ability to produce 7␣-hydroxy-DHEA, and to test the interference of 7␣-and 7␤-hydroxy-DHEA and 7-oxo-DHEA with the 11␤-HSD1-mediated oxidoreduction of cortisol and cortisone. Immuno-histochemical studies showed the presence of both CYP7B1 and 11␤-HSD1 in the liver, skin and tonsils. DHEA was readily 7␣-hydroxylated when incubated using skin slices. A S9 fraction of dermal homogenates containing the 11␤-HSD1 carried out the oxidoreduction of cortisol and cortisone. Inhibition of the cortisol oxidation by 7␣-hydroxy-DHEA and 7␤-hydroxy-DHEA was competitive with a K i at 1.85 ± 0.495 and 0.255 ± 0.005 M, respectively. Inhibition of cortisone reduction by 7-oxo-DHEA was of a mixed type with a K i at 1.13 ± 0.15 M. These findings may support the previously proposed native anti-glucocorticoid paradigm and suggest that the 7␣-hydroxy-DHEA production is a key for the fine tuning of glucocorticoid levels in tissues.

The Journal of Steroid Biochemistry and Molecular Biology, 1997

In many human and murine tissues, both pregnenolone and dehydroepiandrosterone are hydroxylated a... more In many human and murine tissues, both pregnenolone and dehydroepiandrosterone are hydroxylated at the 7~ and 7fl positions by a cytochrome P450-containing microsomal complex. The 7a-and 7fl-hydroxysteroids produced were shown to activate an immune response in mice. Based upon identification by crystallization to constant specific activity and gas chromatography-mass spectrometry analysis, we ascertained that a yeast-expressed human cytochrome P450-1A1 was able to 7fl-hydroxylate pregnenolone (KM from 3.2 + 0.5 to 4.1 _ 0.4 pM, turnover number from 117 ± 15 to 135 ± 13 pmol/min/nrnol of cytochrome P450-1A1). The other human cytochromes P450 tested did not produce identifiable quantities of 7~-or 7fl-hydroxylated derivatives of pregnenolone or dehydroepiandrosterone. These findings indicate that cytochrome P450-1A1 involvement in the 7fl-hydroxylation of pregnenolone may contribute to the production of the 7-hydroxylated steroids necessary for activation of the immune defences. © 1997 Elsevier Science Ltd.

The Journal of Steroid Biochemistry and Molecular Biology, 1997

and characterization of the responsible enzyme system. Using GCIMS, the 7-hydroxylated metabolite... more and characterization of the responsible enzyme system. Using GCIMS, the 7-hydroxylated metabolites of DHEA produced after biotransformation by Fusarium moniliforme mycelia were identified. The strain of Fusariu:m moniliforme hydroxylated DHEA predominantly at the 7~-position, with minor hydroxylation occurring at the 7/~-position. Constitutive 7g-hydroxylation activity was low, but DHEA induced the enzyme complex responsible for 7u-hydroxylation via an increase in protein synthesis. DHEA 7u-hydroxylase was found to be mainly microsomal, and the best production yields of 7g-hydroxy-DHEA (28.5 __ 3.51 pmol/mirdmg protein) were obtained with microsomes prepared from 18-h-induced mycelia. Kinetic parameters (KM=I.18 + 0.035 pNl and Vma~=909 _ 27 pmol/mird mg protein) were determined. Carbon monoxide inhibited 7~-hydroxylation of DHEA by microsomes of Fusarium moniliforme. Also, exposure of mycelia to DHEA increased microsomal P450 content. These results demonstrated that: (i) DHEA is 7~-hydroxylated by microsomes of Fusarium moniliforme; (ii) DHEA induces Fusarium moniliforme 7~-hydroxylase; (iii) this enzyme complex contains a cytochrome P450.

The Journal of Steroid Biochemistry and Molecular Biology, 1999

Transformation of physiologically important 3-hydroxy-steroids by the DHEA-induced 7a-hydroxylase... more Transformation of physiologically important 3-hydroxy-steroids by the DHEA-induced 7a-hydroxylase of F. moniliforme was investigated. Whereas DHEA was almost totally 7a-hydroxylated, PREG, EPIA and ESTR were only partially converted into their 7a-hydroxylated derivatives because hydroxylation at other undetermined positions as well as reduction of ketone at C17 or C20 into hydroxyl also occurred. Cholesterol was not transformed by the enzyme. Kinetic parameters of the 7a-hydroxylation for these substrates were determined and con®rmed that DHEA was the best substrate of the 7a-hydroxylase. Inhibition studies of DHEA 7a-hydroxylation by the other 3-hydroxy-steroids were also carried out and proved that DHEA, PREG, EPIA and ESTR shared the same active site of the enzyme. Induction eects of these steroids were compared, and DHEA appeared to be the best inducer of the 7a-hydroxylase of F. moniliforme. # error of the mean.

The Journal of Steroid Biochemistry and Molecular Biology, 2009

The Journal of Steroid Biochemistry and Molecular Biology, 2008

High dose levels of dehydroepiandrosterone and its 7-hydroxylated derivatives have been shown to ... more High dose levels of dehydroepiandrosterone and its 7-hydroxylated derivatives have been shown to reduce oxidative stress and inflammatory responses in dextran sodium sulfate (DSS)-induced colitis in rats. Another endogenous steroid, 7␤-hydroxy-epiandrosterone (7␤-hydroxy-EpiA) has been shown to exert neuroprotective effects at much smaller doses. Our aims were to evaluate whether 7␤-hydroxy-EpiA pre-treatment prevents DSS-induced colitis and to determine whether the effects involve changes in anti-inflammatory prostaglandin (PG) D 2 and 15-deoxy-12,14 -PGJ 2 (15d-PGJ 2 ) levels. Rats were administered 0.01, 0.1 and 1 mg/kg 7␤-hydroxy-EpiA i.p. once a day for 7 days. Thereafter, colitis was induced by administration of 5% DSS in drinking water for 7 days. Levels of the PGs and the expression of cyclooxygenase (COX-2) and PG synthases were assessed during the course of the experiment. Administration of 7␤-hydroxy-EpiA caused a transient increase in COX-2 and PGE synthase expression within 6-15 h and augmented colonic tissue levels of 15d-PGJ 2 levels starting at day 2. Treatment with DSS resulted in shortened colon length, depleted mucus in goblet cells and induced oxidative stress. COX-2 and mPGES-1 synthase expression were enhanced and accompanied by increased PGE 2 ,D 2 and 15d-PGJ 2 production. Although all dose levels of 7␤-hydroxy-EpiA reduced PGE 2 production, only the lowest dose (0.01 mg/kg) of the steroid completely prevented colitis damage and tissue inflammation. 7␤-Hydroxy-EpiA pre-treatment prevents the occurrence of DSS-induced colitis through a shift from PGE 2 to PGD 2 production, associated with an early but transient increase in COX-2 expression and a sustained increase in the production of the anti-inflammatory prostaglandin 15d-PGJ 2 .

The Journal of Steroid Biochemistry and Molecular Biology, 2004

The human brain is a target tissue for glucocorticoids (GC). Dehydroepiandrosterone (DHEA) is a n... more The human brain is a target tissue for glucocorticoids (GC). Dehydroepiandrosterone (DHEA) is a neurosteroid produced in the brain where it is transformed into 7␣-hydroxy-DHEA and 7␤-hydroxy-DHEA. The antiglucocorticoid effects of both 7-hydroxylated metabolites have been investigated with evidence in mice that neither form of DHEA interfered with the binding of GC to its glucocorticoid receptor (GR), but contributed to a decreased nuclear uptake of the activated GR. Our objective was to use COS-7 cell culture to research DHEA, 7␣-hydroxy-DHEA and 7␤-hydroxy-DHEA interferences with GR trafficking. These cells did not carry out the 7␣-hydroxylation of DHEA and the oxidation of cortisol into cortisone. The cDNA of the human GR was inserted into pcDNA3 for a transient transfection of COS-7 cells. Human GR transactivation activity was measured from a luciferase-MMTV reporter gene. The transfected COS-7 cells were cultured using 10 −12 to 10 −5 M dexamethasone (DEX) or cortisol, which triggered the reporter expression. Treatment with 10 −12 to 10 −5 M DHEA, 7␣hydroxy-DHEA and 7␤-hydroxy-DHEA caused no change in the GC-induced GR transactivation. A reconstruction of the process associated EGFP to the human GR cDNA. Confocal microscopic examination of COS-7 cells transiently expressing the fusion protein EGFP-GR showed nuclear fluorescence 60 min after incubation with 10 −8 M DEX or cortisol. The addition of 10 −5 M DHEA, 7␣-hydroxy-DHEA or 7␤-hydroxy-DHEA did not change its kinesis and intensity. These results contribute to the knowledge of DHEA, 7␣-hydroxy-DHEA and 7␤-hydroxy-DHEA, in relation to antiglucocorticoid activity. We conclude that direct interference with GR trafficking can be discounted in the case of these hormones, therefore proposing new possibilities of investigation.

The Journal of Steroid Biochemistry and Molecular Biology, 2007

The human 11␤-hydroxysteroid dehydrogenase type 1 (11␤-HSD1) catalyzes both the NADP(H)-dependent... more The human 11␤-hydroxysteroid dehydrogenase type 1 (11␤-HSD1) catalyzes both the NADP(H)-dependent oxido-reduction of cortisol and cortisone and the inter-conversion of 7␣-and 7␤-hydroxy-dehydroepiandrosterone (DHEA) through a 7-oxo-DHEA intermediate. As shown with human liver and intestine fractions, 7␣-hydroxy-epiandrosterone (7␣-hydroxy-EpiA) and 7␤-hydroxy-EpiA were readily inter-converted with no evidence for a 7-oxo-EpiA intermediate. Whether this inter-conversion resulted from action of the 11␤-HSD1 or from an unknown epimerase is unresolved. Furthermore, whether these steroids could inhibit the cortisol-cortisone oxido-reduction remains a question. The recombinant human 11␤-HSD1 was used to test these questions. NADP + supplementation only provided the production of 7␤-hydroxy-EpiA out of 7␣-hydroxy-EpiA with a V max /K M ratio at 0.1. With NADPH supplementation, both 7␣-hydroxy-EpiA and 7␤-hydroxy-EpiA were formed in low amounts from 7␤-hydroxy-EpiA and 7␣-hydroxy-EpiA, respectively. These inter-conversions occurred without a trace of the putative 7-oxo-EpiA intermediate. In contrast, the 7-oxo-EpiA substrate was efficiently reduced into 7␣-hydroxy-EpiA and 7␤-hydroxy-EpiA, with V max /K M ratios of 23.6 and 5.8, respectively. Competitive and mixed type inhibitions of the 11␤-HSD1-mediated cortisol oxidation were exerted by 7␣-hydroxy-EpiA and 7␤-hydroxy-EpiA, respectively. The 11␤-HSD1-mediated cortisone reduction was inhibited in a competitive manner by 7-oxo-EpiA. These findings suggest that the active site of the human 11␤-HSD1 may carry out directly the epimeric transformation of 7-hydroxylated EpiA substrates. The low amounts of these steroids in human do not support a physiological importance for modulation of the glucocorticoid status in tissues.

The Journal of Steroid Biochemistry and Molecular Biology, 2004

The cytochrome P4507B1 (P4507B1) in the human hippocampus is responsible for the production of 7␣... more The cytochrome P4507B1 (P4507B1) in the human hippocampus is responsible for the production of 7␣-hydroxylated derivatives of dehydroepiandrosterone (DHEA) and other 3␤-hydroxylated neurosteroids. Minor quantities of the 7␤-hydroxylated derivatives are also produced. Neuroprotective action of these 7-hydroxysteroids was reported. Recombinant human P4507B1 was prepared from yeast coexpressing the human hippocampal P450 cDNA and the human P450 reductase genes. Microsomal P4507B1 activity was tested in the presence of NADPH and 14 C-labeled steroid substrates to deduce kinetic parameters and to study inhibitor responses. The K M values obtained for DHEA, pregnenolone, epiandrosterone, 5␣-androstane-3␤,17␤-diol and estrone were 1.90 ± 0.06, 1.45 ± 0.03, 1.05 ± 0.12, 0.8 ± 0.04 and 1.20 ± 0.26 M, respectively. Production of limited amounts of 7␤-hydroxylated derivatives was also observed, but only with DHEA, 5␣-androstane-3␤,17␤-diol and epiandrosterone. K M values determined for 7␤-hydroxylation were identical to those for 7␣-hydroxylation. The DHEA 7␣-hydroxylation was inhibited by estrone and estradiol (mixed type inhibition) and by the [25-35] ␤-amyloid peptide (non-competitive inhibition). These results indicate that in human, the 7-hydroxylation catalysed by P4507B1 preferentially takes place on DHEA, 5␣-androstane-3␤,17␤-diol and epiandrosterone with major and minor formation of 7␣-and 7␤-hydroxylated derivatives, respectively. Both estrogens and a ␤-amyloid component inhibit the P4507B1-mediated production of the 7-hydroxysteroid metabolites.