Characterization of a Novel Type of Human Microsomal 3α-Hydroxysteroid Dehydrogenase

We report characterization of a novel member of the short chain dehydrogenase/reductase superfamily. The 1513-base pair cDNA encodes a 319-amino acid protein. The corresponding gene spans over 26 kilobase pairs on chromosome 2 and contains five exons. The recombinant protein produced using the baculovirus system is localized in the microsomal fraction of Sf9 cells and is an integral membrane protein with cytosolic orientation of its catalytic domain. The enzyme exhibits an oxidoreductase activity toward hydroxysteroids with NAD+ and NADH as the preferred cofactors. The enzyme is most efficient as a 3α-hydroxysteroid dehydrogenase, converting 3α-tetrahydroprogesterone (allopregnanolone) to dihydroprogesterone and 3α-androstanediol to dihydrotestosterone with similar catalytic efficiency (Vmax values of 13–14 nmol/min/mg microsomal protein and Km values of 5–7 μm). Despite ∼44–47% sequence identity with retinol/3α-hydroxysterol dehydrogenases, the enzyme is not active toward retinols. The corresponding message is abundant in human trachea and is present at lower levels in the spinal cord, bone marrow, brain, heart, colon, testis, placenta, lung, and lymph node. Thus, the new short chain dehydrogenase represents a novel type of microsomal NAD+-dependent 3α-hydroxysteroid dehydrogenase with unique catalytic properties and tissue distribution. We report characterization of a novel member of the short chain dehydrogenase/reductase superfamily. The 1513-base pair cDNA encodes a 319-amino acid protein. The corresponding gene spans over 26 kilobase pairs on chromosome 2 and contains five exons. The recombinant protein produced using the baculovirus system is localized in the microsomal fraction of Sf9 cells and is an integral membrane protein with cytosolic orientation of its catalytic domain. The enzyme exhibits an oxidoreductase activity toward hydroxysteroids with NAD+ and NADH as the preferred cofactors. The enzyme is most efficient as a 3α-hydroxysteroid dehydrogenase, converting 3α-tetrahydroprogesterone (allopregnanolone) to dihydroprogesterone and 3α-androstanediol to dihydrotestosterone with similar catalytic efficiency (Vmax values of 13–14 nmol/min/mg microsomal protein and Km values of 5–7 μm). Despite ∼44–47% sequence identity with retinol/3α-hydroxysterol dehydrogenases, the enzyme is not active toward retinols. The corresponding message is abundant in human trachea and is present at lower levels in the spinal cord, bone marrow, brain, heart, colon, testis, placenta, lung, and lymph node. Thus, the new short chain dehydrogenase represents a novel type of microsomal NAD+-dependent 3α-hydroxysteroid dehydrogenase with unique catalytic properties and tissue distribution. hydroxysteroid dehydrogenase (3-[(3-cholamidopropyl)dimethylammonio]-1-propane-sulfonate high performance liquid chromatography rapid amplification of cDNA ends polymerase chain reaction phosphate-buffered saline retinol dehydrogenase Oxidation and reduction of hydroxyl and ketone groups in position 3 on naturally occurring steroids play an important role in regulation of intracellular levels of biologically active steroid hormones. For example, in gonads, 3α-hydroxysteroid oxidoreductase activity is responsible for maintaining the balance between a potent androgen, 5α-dihydrotestosterone, with a ketone group in position 3 and a weak androgen, 3α-androstanediol, which has a hydroxyl group in the same position (Fig. 1; reviewed in Ref. 1Penning T.M. Pawlowski J.E. Schlegel B.P. Jez J.M. Lin H.K. Hoog S.S. Bennett M.J. Lewis M. Steroids. 1996; 61: 508-523Crossref PubMed Scopus (66) Google Scholar). In the central nervous system, 3α-hydroxysteroid oxidoreductase activity controls the amount of a potent neurosteroid, 3α-tetrahydroprogesterone (also called allopregnanolone), which serves as an allosteric regulator of all γ-aminobutyric acid type A receptors and potentiates γ-aminobutyric acid mediated chloride conductance (1Penning T.M. Pawlowski J.E. Schlegel B.P. Jez J.M. Lin H.K. Hoog S.S. Bennett M.J. Lewis M. Steroids. 1996; 61: 508-523Crossref PubMed Scopus (66) Google Scholar). 3α-Hydroxysteroid oxidoreductase activity has been described in the cytosolic and microsomal fractions of a number of human and animal tissues (2Verhoeven G. Heyns W. De Moor P. J. Steroid Biochem. 1977; 8: 731-733Crossref PubMed Scopus (25) Google Scholar, 3Verhoeven G. Heyns W. De Moor P. Eur. J. Biochem. 1976; 65: 565-576Crossref PubMed Scopus (32) Google Scholar, 4Krause J.E. Karavolas H.J. J. Biol. 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In addition to the different subcellular localization, cytosolic and microsomal enzymes appear to have a distinctively different cofactor preference. Cytosolic 3α-hydroxysteroid oxidoreductases exhibit a preference for the phosphorylated nucleotides as cofactors (NADP+/NADPH), whereas microsomal enzymes prefer NAD+/NADH (2Verhoeven G. Heyns W. De Moor P. J. Steroid Biochem. 1977; 8: 731-733Crossref PubMed Scopus (25) Google Scholar, 3Verhoeven G. Heyns W. De Moor P. Eur. J. Biochem. 1976; 65: 565-576Crossref PubMed Scopus (32) Google Scholar, 4Krause J.E. Karavolas H.J. J. Biol. Chem. 1980; 255: 11807-11814Abstract Full Text PDF PubMed Google Scholar, 5Krause J.E. Karavolas H.J. J. Steroid Biochem. 1981; 14: 63-69Crossref PubMed Scopus (18) Google Scholar, 6Pirog E.C. Collins D.C. Steroids. 1994; 59: 259-264Crossref PubMed Scopus (13) Google Scholar, 7Span P.N. Sweep C.G.J. Benraad Th.J. Smals A.G.H. J. Steroid Biochem. Mol. Biol. 1996; 58: 319-324Crossref PubMed Scopus (17) Google Scholar, 8Li X. Bertics P.J. Karavolas H.J. J. Steroid Biochem. Mol. Biol. 1997; 60: 311-318Crossref PubMed Scopus (87) Google Scholar, 9Dombroski R.A. Casey M.L. MacDonald P.C. J. Steroid Biochem. Mol. Biol. 1997; 63: 155-163Crossref PubMed Scopus (44) Google Scholar, 10Pirog E.C. Collins D.C. J. Clin. Endocrinol. Metab. 1999; 84: 3217-3221PubMed Google Scholar, 11Ge R.S. Hardy D.O. Catterall J.F. Hardy M.P. Biol. Reprod. 1999; 60: 855-860Crossref PubMed Scopus (39) Google Scholar). Because the predominant forms of nucleotide cofactors in the cells are NAD+ and NADPH, it is generally believed that the NAD+-dependent dehydrogenases function mainly in the oxidative direction, whereas the NADPH-dependent enzymes function as reductases (12Labrie F. Luu-The V. Lin S.-X. Labrie C. Simard J. Breton R. Belanger A. Steroids. 1997; 62: 148-158Crossref PubMed Scopus (428) Google Scholar). Thus, the balance between the oxidative and reductive activities will determine the local concentrations of bioactive compounds in specific tissues. To date, at least four types of cytosolic 3α-hydroxysteroid dehydrogenases (HSDs)1 have been identified in humans (1Penning T.M. Pawlowski J.E. Schlegel B.P. Jez J.M. Lin H.K. Hoog S.S. Bennett M.J. Lewis M. Steroids. 1996; 61: 508-523Crossref PubMed Scopus (66) Google Scholar, 13Penning T.M. Burczynski M.E. Jez J.M. Hung C.F. Lin H.K. Ma H. Moore M. Palackal N. Ratnam K. Biochem. J. 2000; 351: 67-77Crossref PubMed Scopus (553) Google Scholar, 14Khanna M. Qin K.N. Wang R.W. Cheng K.C. J. Biol. Chem. 1995; 270: 20162-20168Abstract Full Text Full Text PDF PubMed Scopus (174) Google Scholar). All four cytosolic enzymes, named AKR1C1-AKR1C4, are members of the aldo-ketoreductase gene superfamily and prefer NADPH as cofactor (13Penning T.M. Burczynski M.E. Jez J.M. Hung C.F. Lin H.K. Ma H. Moore M. Palackal N. Ratnam K. Biochem. J. 2000; 351: 67-77Crossref PubMed Scopus (553) Google Scholar). Liver is the only tissue that contains all four isoforms at similar levels (13Penning T.M. Burczynski M.E. Jez J.M. Hung C.F. Lin H.K. Ma H. Moore M. Palackal N. Ratnam K. Biochem. J. 2000; 351: 67-77Crossref PubMed Scopus (553) Google Scholar). Extrahepatic tissues such as lung, prostate, uterus, mammary gland, brain, small intestine, and testis vary significantly in their composition and relative amounts of individual isoforms (13Penning T.M. Burczynski M.E. Jez J.M. Hung C.F. Lin H.K. Ma H. Moore M. Palackal N. Ratnam K. Biochem. J. 2000; 351: 67-77Crossref PubMed Scopus (553) Google Scholar). The identity of the enzymes responsible for the NAD+-dependent 3α-hydroxysteroid oxidoreductase activity found in microsomes has remained elusive until recently, when several newly discovered members of the short chain dehydrogenase/reductase superfamily were shown to stereospecifically oxidize the 3α-hydroxyl group on 3α-androstanediol (15Biswas M.G. Russell D.W. J. Biol. Chem. 1997; 272: 15959-15966Abstract Full Text Full Text PDF PubMed Scopus (217) Google Scholar, 16Wang J. Chai X. Eriksson U. Napoli J.L. Biochem. J. 1999; 338: 23-27Crossref PubMed Scopus (76) Google Scholar, 17Chai X. Zhai Y. Napoli J.L. J. Biol. Chem. 1997; 272: 33125-33131Abstract Full Text Full Text PDF PubMed Scopus (81) Google Scholar, 18Su J. Chai X. Kahn B. Napoli J.L. J. Biol. Chem. 1998; 273: 17910-17916Abstract Full Text Full Text PDF PubMed Scopus (70) Google Scholar, 19Su J. Lin M. Napoli J.L. Endocrinology. 1999; 140: 5275-5284Crossref PubMed Scopus (56) Google Scholar, 20Gough W.H. Van Ooteghem S. Sint T. Kedishvili N.Y. J. Biol. Chem. 1998; 273: 19778-19785Abstract Full Text Full Text PDF PubMed Scopus (110) Google Scholar) and allopregnanolone J. W.H. N. Kedishvili N.Y. Biochem. PubMed Scopus Google Scholar, Luu-The V. J. Biol. Chem. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar). In to cytosolic short chain dehydrogenases exhibit a preference for NAD+ as the properties of human microsomal short chain dehydrogenases that are of 3α-androstanediol to and allopregnanolone to W.H. Van Ooteghem S. Sint T. Kedishvili N.Y. J. Biol. Chem. 1998; 273: 19778-19785Abstract Full Text Full Text PDF PubMed Scopus (110) Google Scholar, J. W.H. N. Kedishvili N.Y. Biochem. PubMed Scopus Google Scholar). The of for enzymes and is not to oxidize and to the of a potent acid W.H. Van Ooteghem S. Sint T. Kedishvili N.Y. J. Biol. Chem. 1998; 273: 19778-19785Abstract Full Text Full Text PDF PubMed Scopus (110) Google Scholar, J. W.H. N. Kedishvili N.Y. Biochem. PubMed Scopus Google Scholar). and human dehydrogenase shown to oxidize with lower catalytic efficiency J. Chai X. Eriksson U. Napoli J.L. Biochem. J. 1999; 338: 23-27Crossref PubMed Scopus (76) Google Scholar). found to on the of the A. A. J.M. Eriksson U. J. 1999; PubMed Google Scholar) and in the of H. A. Eriksson U. 1999; PubMed Scopus Google the cofactor for and the for receptors R. S. J. Biol. Chem. 1997; 272: Full Text Full Text PDF PubMed Scopus Google Scholar). The human dehydrogenases acid sequence similar and on chromosome enzymes exhibit distinctively different tissue is in human and W.H. Van Ooteghem S. Sint T. Kedishvili N.Y. J. Biol. Chem. 1998; 273: 19778-19785Abstract Full Text Full Text PDF PubMed Scopus (110) Google Scholar, V. N. J. Napoli J.L. M. Mol. Metab. 1999; PubMed Scopus Google Scholar). is present in lung, prostate, testis, (15Biswas M.G. Russell D.W. J. Biol. Chem. 1997; 272: 15959-15966Abstract Full Text Full Text PDF PubMed Scopus (217) Google spinal J. W.H. N. Kedishvili N.Y. Biochem. PubMed Scopus Google and of human J. W.H. N. Kedishvili N.Y. Biochem. PubMed Scopus Google Scholar). to in a of mammary gland, colon, small intestine, and J. Chai X. Eriksson U. Napoli J.L. Biochem. J. 1999; 338: 23-27Crossref PubMed Scopus (76) Google R. S. J. Biol. Chem. 1997; 272: Full Text Full Text PDF PubMed Scopus Google Scholar). contains the levels of for all report and characterization of a novel human 3α-hydroxysteroid We in to the identified enzymes, human 3α-hydroxysteroid dehydrogenase is not active toward and exhibits different membrane as as different tissue distribution. cDNA identified in the sequence of on its to human of the that it the at nucleotide in The rapid amplification of cDNA ends using human cDNA as The and in were on the sequence of The were with the and the cDNA in polymerase The were for as at for at for and at for The pair cDNA and cDNA and pairs of the The nucleotide sequence to with number To the human and were using polymerase and is and is of amplification were as at for at for and at for The were of The were to the cDNA sequence of the gene of The of the and were The of the corresponding gene using the cDNA sequence and the The tissue were for and which a of of The were with pair cDNA in to the the were in for at and to a 2 The at for The were in several at and in for at The were to at with for of the cDNA in Sf9 cells as described W.H. Van Ooteghem S. Sint T. Kedishvili N.Y. J. Biol. Chem. 1998; 273: 19778-19785Abstract Full Text Full Text PDF PubMed Scopus (110) Google Scholar). To recombinant Sf9 cells were at a of were 3 of at in and and and using a The and were at for and were at for were at for a and in and the of J. Biol. Chem. Full Text PDF PubMed Google Scholar) using as a of microsomes the recombinant protein were with of and with phosphate-buffered saline with in for on were of in and for at were in of were with an of acid for on and for 3 at The were with and in of in a were to membrane using the system to the the of were as at a in and using a and All were in and at in as described W.H. Van Ooteghem S. Sint T. Kedishvili N.Y. J. Biol. Chem. 1998; 273: 19778-19785Abstract Full Text Full Text PDF PubMed Scopus (110) Google Scholar). steroids were with steroids and in The of were with the addition of at steroids were and in on steroids were to a which were in liquid of reaction were identified with For of concentrations between and were for allopregnanolone and and concentrations between and were for and The amount of of the amount of the reaction and to the amount of microsomes A cofactor with and The Km values for of hydroxysteroids were at a and the for reduction of dihydrotestosterone at a NADH at least The Km values for cofactors were at a of with concentrations of cofactor for NAD+ and for The activity with and in the same reaction for steroid The reaction to for at and the reaction were and as described J. W.H. N. Kedishvili N.Y. Biochem. PubMed Scopus Google Scholar). The of the cDNA of the of The cDNA for C. P.C. J. Biol. Chem. Full Text PDF PubMed Google Scholar) human cDNA using polymerase and and which and The of and and to the of The were to in polymerase and in in the of microsomes to the In a of of and of microsomal were for at in a of of to the of the microsomes of the in were for on with in a of the addition of were to and of microsomes Sf9 cells were with in the of were at for with amounts of relative to microsomal protein in a reaction of The reaction the addition of to the of 2 of the reaction were and activity using as The 1513-base pair cDNA shown in 2 the of the and the in The at nucleotide and ends in a at nucleotide in a 319-amino A of the for that exhibit to the cDNA human retinol dehydrogenase gene retinol dehydrogenase and H. retinol dehydrogenase The cDNA is to and in the cDNA shown in 2 is a for between and in it contains nucleotides of the sequence with an pair dehydrogenase pairs for between and whereas has an of nucleotides between and in the (Fig. as as four nucleotides and which a To the cDNA and the cDNA and protein amplification of human and heart, using the of the that were with the sequence in a of the that the cDNA sequence in is to five in the to chromosome The corresponding gene spans over 26 kilobase pairs and not appear to have The the and are in of human microsomal in a new The protein sequence of the novel protein contains the cofactor at and the active sequence at of the short chain The acid sequence is most to dehydrogenases of the short chain dehydrogenase/reductase and the of in the of the novel gene and the of 3 and are to in the for and (Fig. 3 the new gene is present on chromosome whereas dehydrogenases are on chromosome N.Y. W.H. Chem. Biol. 2000; Scholar). of the corresponding message of with cDNA that the message for the short chain dehydrogenase is present in a number of human tissues (Fig. The most in were in spinal cord, bone marrow, heart, and were present in lymph brain, lung, placenta, testis, prostate, and mammary A of were which The were in testis, and present in colon, placenta, lung, bone marrow, and lymph with amounts in mammary gland, prostate, and The in spinal cord, lymph brain, bone marrow, and To the novel cDNA for a the corresponding protein using the baculovirus to human dehydrogenases, the recombinant protein present in the microsomal fraction of Sf9 cells as using the of the same protein were in microsomes Sf9 cells with which not the recombinant protein not To determine the new short chain dehydrogenase is an integral membrane microsomal fraction Sf9 cells that the recombinant protein to and amounts of microsomes were with were and shown in the recombinant protein remained of a with the of an integral membrane protein. the short chain dehydrogenase is Because its acid sequence the to dehydrogenases, it a hydroxysteroid dehydrogenase activity using reaction for W.H. Van Ooteghem S. Sint T. Kedishvili N.Y. J. Biol. Chem. 1998; 273: 19778-19785Abstract Full Text Full Text PDF PubMed Scopus (110) Google Scholar) and J. W.H. N. Kedishvili N.Y. Biochem. PubMed Scopus Google Scholar). were with a number of steroid compounds for at in the of NAD+ The reaction were and using a a of the of in the oxidative in the of NAD+ with 3α-androstanediol and allopregnanolone contains hydroxyl groups in and (Fig. The enzyme and as the of with ketone groups in 3 and (Fig. To the relative efficiency of the that have only hydroxyl 3α-hydroxyl (Fig. The 3α-hydroxyl group to the group to To the activity of the as in of were that the of not to the of the for the novel in the oxidative allopregnanolone a amount of dihydroprogesterone with ketone group in position an in that the ketone group on 3 of dihydroprogesterone to a type of activity of with allopregnanolone and NAD+ Luu-The V. J. Biol. Chem. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar). of the reaction in the reductive in the of NADH that ketone group on 3 to hydroxyl group with the catalytic efficiency to (Fig. The group on at a To that the and dehydrogenase activity not to activity of the activity of microsomes Sf9 cells that were with and not a of and of were 3 of microsomes dihydrotestosterone and in the of In the same amount of microsomes that produced of and of The hydroxysteroid activity of Sf9 microsomes the cells with using in the of NAD+ dehydrogenase NADH shown in were in the oxidative the reductive on that all of the steroid were the novel for and reduction of NAD+ and NADH in the preferred cofactors. In the oxidative direction, using allopregnanolone as the reaction in the of in the of In the reductive direction, using dihydrotestosterone as the with NADH it with Thus, NAD+ and NADH were the preferred cofactors. The Km for NAD+ with The for NADH with dihydrotestosterone that are the enzyme over of with high enzyme which only reaction were to determine for steroid the values for allopregnanolone and 3α-androstanediol were when of and with of the reaction allopregnanolone and were the in the oxidative with the of 5–7 The for that the enzyme of the of lower with that of allopregnanolone which the corresponding not using a (Fig. to with a catalytic efficiency similar to that for the of 3α-hydroxyl group for steroid microsomal were in and at for dihydrotestosterone with and the Km values for all were with in a new were in and at for dihydrotestosterone with and the Km values for all were with To determine the new enzyme active toward of microsomal the recombinant protein with in the of a at the reaction were and as described J. W.H. N. Kedishvili N.Y. Biochem. PubMed Scopus Google Scholar). The amount of the of the amount of the on were produced of microsomal protein over the For of dihydroprogesterone have been produced allopregnanolone the same amount of protein the that the of retinol is at least lower that of the new enzyme is not efficient as retinol Because have that the novel is an integral membrane were in its of its protein sequence for and that is a as as at and Because is on the of the the of protein with in the of microsomes that and were to the To the of a in system and microsomal a protein with orientation and A. P. A. J. Biol. Chem. 1999; Full Text Full Text PDF PubMed Scopus (174) Google as a for in in the of of the reaction that the of produced in the of microsomes to that produced in the of that the in were not the same all were in the the reaction were with to determine the protein the membrane and the In with the of produced in the of microsomes not whereas the is with the cytosolic orientation of in to the orientation for A. P. A. J. Biol. Chem. 1999; Full Text Full Text PDF PubMed Scopus (174) Google Scholar). To for the cytosolic orientation of the new microsomes Sf9 cells with different concentrations of in the of and the activity and the amount of protein in the and of that the of membrane not for to (Fig. The activity of the enzyme with nmol/min/mg microsomal protein to nmol/min/mg microsomal protein at a in activity protein in the of K. on the that the new short chain dehydrogenase is an integral membrane which the cytosolic of the microsomal The novel in the present exhibits acid sequence identity to protein. is most to dehydrogenases of the short chain dehydrogenase/reductase superfamily. the gene for similar with the for dehydrogenases N.Y. W.H. Chem. Biol. 2000; Scholar). is in the of which is acid that the corresponding in the gene and 2 that in the and gene is found on a different chromosome and not appear to have and N.Y. W.H. Chem. Biol. 2000; which that it in of the in the sequence that cDNA to different of cDNA were lymph testis and and and Thus, to exhibit tissue distribution. of human tissues that is present in the central nervous system and in a number of tissues. the of the predominant on the tissue that a of In found that the in the sequence of a the of retinol dehydrogenase is the pair sequence of that The most in the of the novel with that of dehydrogenases is that the message is in The of with the serves as a that the cDNA not with of which are abundant in the The of in the is with its activity toward which serves as a potent allosteric regulator of γ-aminobutyric acid type A is to produced in the cytosolic and which the reduction of the group on dihydroprogesterone (13Penning T.M. Burczynski M.E. Jez J.M. Hung C.F. Lin H.K. Ma H. Moore M. Palackal N. Ratnam K. Biochem. J. 2000; 351: 67-77Crossref PubMed Scopus (553) Google Scholar). The of allopregnanolone to dihydroprogesterone is to an NAD+-dependent J.E. Karavolas H.J. J. Biol. Chem. 1980; 255: 11807-11814Abstract Full Text PDF PubMed Google Scholar, 5Krause J.E. Karavolas H.J. J. Steroid Biochem. 1981; 14: 63-69Crossref PubMed Scopus (18) Google Scholar). have that is of allopregnanolone and is in of the human and in the spinal J. W.H. N. Kedishvili N.Y. Biochem. PubMed Scopus Google that it function as allopregnanolone dehydrogenase in the central nervous in addition to the central nervous system contains a of microsomal oxidative active toward similar to J. W.H. N. Kedishvili N.Y. Biochem. PubMed Scopus Google Scholar, Luu-The V. J. Biol. Chem. 2000; Full Text Full Text PDF PubMed Scopus Google the newly enzyme exhibits activity toward converting it to in the of We have that which is produced of in the active and the reduction of the group on dihydroprogesterone to a 3α-hydroxyl and a with the new exhibits a for NADH for NAD+ Km is similar to J. W.H. N. Kedishvili N.Y. Biochem. PubMed Scopus Google Scholar). the same which has Km values for NAD+ and NADH not to the V. and N. Y. in addition to not of with the new to the Km of the enzyme for with allopregnanolone as the new is efficient at converting 3α-androstanediol a potent androgen, is with the of the enzyme in testis and and Russell (15Biswas M.G. Russell D.W. J. Biol. Chem. 1997; 272: 15959-15966Abstract Full Text Full Text PDF PubMed Scopus (217) Google Scholar) that which is in and testis, to the of 3α-androstanediol to dihydrotestosterone in tissues. in addition to dihydrotestosterone produced in testis and the novel of to dehydrogenases, is an integral membrane protein. on its the active of the enzyme to the to the of the in its to the and cofactors. of the of which to the of in that is to the of A. A. J.M. Eriksson U. J. 1999; PubMed Google Scholar). The catalytic of enzyme is to the that of in the of the A. A. J.M. Eriksson U. J. 1999; PubMed Google Scholar). In to to the cytosolic of the that it will the cytosolic of steroids and In the and in the is whereas the is Biochem. J. PubMed Scopus Google Scholar). that the which the the new will function in the oxidative The and cofactor for the which NAD+ over as cofactor A. U. C. Eriksson U. J. Biol. Chem. 1995; 270: Full Text Full Text PDF PubMed Scopus Google is The of enzymes that similar exhibit different orientation is not For example, members of the short chain dehydrogenase/reductase type and type which the between a potent and a weak exhibit type is a whereas type 2 the A. P. A. J. Biol. Chem. 1999; Full Text Full Text PDF PubMed Scopus (174) Google Scholar). enzymes exhibit a different cofactor type and reduction using as whereas type 2 is and only is in to and which appear to exhibit a cofactor preference for the in the and tissue exhibits different with and the microsomal dehydrogenases, and has similar for of for and and 3α-androstanediol of J. Chai X. Eriksson U. Napoli J.L. Biochem. J. 1999; 338: 23-27Crossref PubMed Scopus (76) Google Scholar) and is efficient as retinol dehydrogenase as a steroid and an position and are efficient as 3α-hydroxysteroid dehydrogenases with Km values of W.H. Van Ooteghem S. Sint T. Kedishvili N.Y. J. Biol. Chem. 1998; 273: 19778-19785Abstract Full Text Full Text PDF PubMed Scopus (110) Google Scholar, J. W.H. N. Kedishvili N.Y. Biochem. PubMed Scopus Google Scholar) the of J. W.H. N. Kedishvili N.Y. Biochem. PubMed Scopus Google Scholar). The new is with compounds and is most efficient as allopregnanolone and 3α-androstanediol dehydrogenase, the of the Thus, in that the new member of the short chain dehydrogenase/reductase superfamily is a novel type of microsomal NAD+-dependent with unique tissue and catalytic We of and of for and of the