Characterization of bovine liver cytosolic 3 alpha-hydroxysteroid dehydrogenase and its aldo-keto reductase activity

Opposing changes in 3alpha-hydroxysteroid dehydrogenase oxidative and reductive activities in rat leydig cells during pubertal development

The enzyme 3alpha-hydroxysteroid dehydrogenase (3alpha-HSD) has an important role in androgen metabolism, catalyzing the interconversion of dihydrotestosterone (DHT) and 5alpha-androstane-3alpha,17beta-diol (3alpha-DIOL). The net direction of this interconversion will affect the amount of biologically active ligand available for androgen receptor binding. We hypothesize that in Leydig cells, differential expression of 3alpha-HSD enzymes favoring one of the two directions is a mechanism by which DHT levels are controlled. In order to characterize 3alpha-HSD in rat Leydig cells, the following properties were analyzed: rates of oxidation (3alpha-DIOL to DHT) and reduction (DHT to 3alpha-DIOL) and preference for the cofactors NADP(H) and NAD(H) (i.e., the oxidized and reduced forms of both pyridine nucleotides) in Leydig cells isolated on Days 21, 35, and 90 postpartum. Levels of 3alpha-HSD protein were measured by immunoblotting using an antibody directed against the liver type of the enzyme. Levels of 3alpha-HSD protein and rates of reduction were highest on Day 21 and lowest on Day 90. The opposite was true for the rate of 3alpha-HSD oxidation, which was barely detectable on Day 21 and highest on Day 90 (59.08 +/- 6.35 pmol/min per 10(6) cells, mean +/- SE). Therefore, the level of 3alpha-HSD protein detectable by liver enzyme was consistent with reduction but not with oxidation. There was a clear partitioning of NADP(H)-dependent activity into the cytosolic fraction of Leydig cells, whereas on Days 35 and 90, Leydig cells also contained a microsomal NAD(H)-activated 3alpha-HSD. We conclude that 1) the cytosolic 3alpha-HSD in Leydig cells on Day 21 behaves as a unidirectional NADPH-dependent reductase; 2) by Day 35, a microsomal NAD(H)-dependent enzyme activity is present and may account for predominance of 3alpha-HSD oxidation over reduction and the resultant high capacity of Leydig cells on Day 90 to synthesize DHT from 3alpha-DIOL.

The role of cysteine in the alteration of bovine liver dihydrodiol dehydrogenase 3 activity

Bovine liver NADP(+)-dependent dihydrodiol dehydrogenase (DD3) is extremely sensitive to SH reagents such as N-ethylmaleimide (NEM) and 5,5'-dithiobis(2-nitrobenzoic acid). NEM produced time- and concentration-dependent inactivation of DD3 in a pseudo-first-order reaction manner. This inactivation was prevented by NADP+, 3-acetylpyridine-adenine dinucleotide phosphate, 2',5'-ADP and 2'-AMP but not by substrates, NAD+, nicotinamide mononucleotide or 5'-ADP.DD3 was absorbed by an affinity column of thiopropyl-Sepharose 6B, but enzyme incubated with both NEM and NADP+ was not. Moreover, one [14C]NEM molecule was incorporated into a cysteine of DD3 in the presence, and two cysteines of DD3 in the absence, of NADP+. These results suggested that two cysteine residues were modified per enzyme molecule by NEM, one was protected by NADP+ and the other had no significant function for the enzyme activity. Two radiolabelled peptides (P1 and P2) produced by the digestion with lysyl endopeptidase of [14C]NEM-modified DD3 could be separated by reverse-phase HPLC. P1, which was radiolabelled by [14C]NEM only in the absence of NADP+, showed the following sequence; H2N-Tyr-Lys-Pro-Val-Xaa-Asn-Gln-Val-Glu- NEM.Cys-His-Pro-Tyr-Phe-Asn-Gln-Ser-Lys-COOH (Xaa indicates a possible cysteine residue). This sequence was very similar to that of rat liver 3 alpha-hydroxysteroid/dihydrodiol dehydrogenase (3 alpha-HSD/DD) (residues 184 to 201) and was also highly conserved in the aldo-keto reductase superfamily. The sequence of P2, which had radioactivity in both the absence and presence of NADP+, also contained an NEM-modified cysteine and was similar in sequence to the regions located in loop A of rat 3 alpha-HSD/DD. The present study suggests that P1, which may have a cysteine residue corresponding to Cys-193 of rat 3 alpha-HSD/DD, functions in the alteration of DD3 activity depending on the modulation of NADP(+)-binding ability through a thiol/disulphide exchange reaction similar to that of rat 3 alpha-HSD/DD shown in our previous results; while P2, which may have a cysteine residue corresponding to Cys-145 of rat 3 alpha-HSD/DD, may be located near the surface of the enzyme molecule.

Enzymatic characterization of a novel bovine liver dihydrodiol dehydrogenase--reaction mechanism and bile acid dehydrogenase activity

Bovine liver cytosolic dihydrodiol dehydrogenase (DD3) has been characterized by its unique dihydrodiol dehydrogenase activity for trans-benzenedihydrodiol (trans-1,2-dihydrobenzene-1,2-diol) with the highest affinity and the greatest velocity among three multiple forms of dihydrodiol dehydrogenases (DD1-DD3). It is the first time that DD3 has shown a significant dehydrogenase activity for (S)-(+)-1-indanol with low Km value (0.33 +/- 0.022 mM) and high K(cat) value (25 +/- 0.79 min-1). The investigation of the product inhibition of (S)-(+)-1-indanol with NADP+ versus 1-indanone and NADPH clearly showed that the enzymatic reaction of DD3 may follow a typical ordered Bi Bi mechanism similar to many aldo/keto reductases. Additionally, DD3 was shown to catalyze the dehydrogenation of bile acids (lithocholic acid, taurolithocholic acid and taurochenodeoxycholic acid) having no 12-hydroxy groups with low Km values (17 +/- 0.65, 33 +/- 1.9 and 890 +/- 73 microM, respectively). In contrast, DD1, 3 alpha-hydroxysteroid dehydrogenase, shows a broad substrate specificity for many bile acids with higher affinity than those of DD3. Competitive inhibition of DD3 with androsterone against dehydrogenase activity for (S)-(+)-1-indanol, trans-benzenedihydrodiol or lithocholic acid suggests that these three substrates bind to the same substrate binding site of DD3, different from the case of human liver bile acid binder/dihydrodiol dehydrogenase (Takikawa, H., Stolz, A., Sugiyama, Y., Yoshida, H., Yamamoto, M. and Kaplowitz, N. (1990) J. Biol. Chem. 265, 2132-2136). Considering the reaction mechanism, DD3 may also play an important role in bile acids metabolism as well as the detoxication of aromatic hydrocarbons.

Role of lysine residues in the nucleotides binding to bovine liver high-Km aldehyde reductase

The inactivation of bovine liver high-Km aldehyde reductase (ALR) by heat (47 degrees C), 0.3 mM 2,4,6-trinitrobenzene sulfonate (TNBS) and 0.03 mM pyridoxal 5'-phosphate (PAL-P) followed pseudo-first-order kinetic as a function of incubation-time and concentration of TNBS. Nucleotides which have a 2'-phosphate group, especially beta-NADPH and beta-NADP+, showed effective protection on ALR-inactivation. However, typical substrates for ALR such as D,L-glyceraldehyde, D-erythrose, D-glucuronate and p-carboxybenzaldehyde could not protect the enzyme from inactivation. Completely inactivated enzyme was estimated to have 2.07 TNBS-modified lysine residues/mol enzyme from the determination of free amino group using fluorescamine (Ex = 390 nm, Em = 475 nm). Enzyme protected by beta-NADP+ (96.5% remaining activity) did not lose a significant number of lysine residues. Kd-values for beta-NADPH and beta-NADP+ were estimated to be 0.48 microM and 4.7 microM, respectively and TNBS-treated enzyme lost its ability to bind to these nucleotides.

Purification and characterization of carbonyl reductases from bovine liver cytosol and microsome. The cytosolic enzyme has a novel 3 alpha/17 beta-hydroxysteroid dehydrogenase activity

1. Carbonyl reductase, which is distributed in both cytosolic and microsomal fractions in bovine liver, were purified to homogeneity on 12.5% sodium dodecylsulfate-polyacrylamide gel electrophoresis and shown to have molecular weights of 32 kDa and 68 kDa, respectively. 2. Both carbonyl reductases can catalyze the reduction of many carbonyl compounds including ketone, quinones and aldehyde with relatively low Km values. 3. From the absorption spectrum result, microsomal carbonyl reductase closely resembles cytochrome P-450 reductase. 4. Cytosolic carbonyl reductase is a novel enzyme which can act on both testosterone and androsterone at low concentration.

Modulation of 3 alpha-hydroxysteroid dehydrogenase activity by the redox state of glutathione

3 alpha-Hydroxysteroid dehydrogenase (EC 1.1.1.50), purified to homogeneity from rat liver, was strongly inactivated by incubation with a disulfide such as GSSG, L-cystine or L-cystamine, as well as an SH-reagent such as DTNB (5,5'-dithiobis(2-nitrobenzoic acid)), NEM (N-ethylmaleimide) or iodoacetic acid. The inactivation advanced with incubation time. Coenzyme (NADP+) completely protected the enzyme from this inactivation by disulfides, but neither of the substrates (androsterone and benzenedihydrodiol) did. The activity of inactivated enzyme was restored by treatment with thiols such as DTT (dithiothreitol) or GSH. In the GSH/GSSG redox buffer, the enzyme existed in an equilibrium between active (reduced) and inactive (oxidized) forms.