Toshihiro Nakayama

Reductases for carbonyl compounds in human liver

Two aldehyde reductases with mol. wt 78,000 and 32,000 and one carbonyl reductase with mol. wt 31,000 were purified to homogeneity from human liver cytosol. The high molecular weight aldehyde reductase exhibited properties similar to alcohol dehydrogenase; it had a single subunit of mol. wt 41,000 and a pI value of 10 to 10.5, and showed preference for NADH over NADPH as cofactor and sensitivity to SH-reagents, pyrazole, o-phenanthroline and isobutyramide. The enzyme reduced aliphatic and aromatic aldehydes, alicyclic ketones and alpha-diketones and an optimal pH of 6.0, and oxidized various alcohols with NAD as a cofactor at an optimal pH of 8.8. The identity of the enzyme with alcohol dehydrogenase was established by starch gel electrophoresis and co-purification of the two enzymes. The other enzymes were NADPH-dependent and monomeric reductases; the aldehyde reductase reduced aldehydes, hexonates and alpha-diketones and was sensitive to barbiturates, diphenylhydantoin and valproate, while the carbonyl reductase showed a broad substrate specificity for aldehydes, ketones and quinones and was inhibited by SH-reagent, quercitrin and benzoic acid. The latter enzyme appeared in three multiforms with different charges which occurred in differing ratios in liver specimens. Comparison of kinetic constants for aldehydes among the enzymes indicated that alcohol dehydrogenase is the best reductase with the highest affinity and Kcat values. The enzyme also catalyzed oxidation and reduction of aromatic aldehydes in the presence of NAD at physiological pH of 7.2. Tissue distribution of the three enzymes and variation of their specific activities in human livers were examined.

Mouse liver dihydrodiol dehydrogenases: Identity of the predominant and a minor form with 17β-hydroxysteroid dehydrogenase and aldehyde reductase

A major and a minor form of dihydrodiol dehydrogenase were co-purified with 17 beta-hydroxysteroid dehydrogenase and aldehyde reductase, respectively, to apparent homogeneity from liver cytosol of male ddY mice. The activities of dihydrodiol dehydrogenase and testosterone dehydrogenase or aldehyde reductase of the two enzyme forms comigrated electrophoretically. The major form of the enzyme oxidized 17 beta-hydroxysteroids and nonsteroidal alicyclic alcohols and reduced 17-ketosteroids and various synthetic carbonyl compounds, showing higher affinity for steroids than for xenobiotics. The activity of this enzyme form toward benzene dihydrodiol and testosterone exhibited identical thermostability and susceptibility to inhibition by quercitrin, SH-reagents, nonsteroidal estrogens and anti-inflammatory agents. On the other hand, the minor form of the enzyme, which oxidized benzene dihydrodiol but not 17 beta-hydroxysteroids, also reduced various aldehydes well and was specifically inhibited by barbiturates and sorbinil. These results indicate that the major form of dihydrodiol dehydrogenase is identical to 17 beta-hydroxysteroid dehydrogenase and the minor enzyme form to aldehyde reductase.

Characterization of pulmonary carbonyl reductase of mouse and guinea pig.

Carbonyl reductases were purified from mouse and guinea pig lung. The mouse enzyme exhibited structural and catalytic similarity to the guinea pig enzyme: tetrameric structure consisting of an identical 23 kDa subunit; basicity (pI of 8.8); low substrate specificity for aliphatic and aromatic carbonyl compounds; dual cofactor specificity for NADPH and NADH; stereospecific transfer of the 4-pro S hydrogen of NADPH; and sensitivity to pyrazole, 2-mercaptoethanol and ferrous ion. Although 3-ketosteroids were extensively reduced by the mouse enzyme but not by the guinea pig enzyme in the forward reaction, the two enzymes similarly oxidized some alicyclic alcohols such as acenaphthenol, cyclohex-2-en-1-ol and benzenedihydrodiol in the presence of NADP+ and NAD+. A partial similarity between the two enzymes was observed immunologically, using antibodies against the purified guinea pig enzyme. The lung enzymes differ in several aspects from other oxidoreductases from extrapulmonary tissues. The immunoreactive protein was detected only in lung of the tissues of the two species.

Purification and characterization of a novel pyrazole-sensitive carbonyl reductase in guinea pig lung☆

Abstract NADPH-dependent aldehyde reductase activity in the cytosol of guinea pig lung can be separated into two enzyme species by gel filtration on Sephadex G-100. The major enzyme, purified to homogeneity, has an apparent M r of 86,000 and is composed of single subunits with M r of 23,000. The isoelectric point of this enzyme is 9.8. The enzyme reduces not only aliphatic and aromatic aldehydes and ketones but also quinones. The low reverse reaction is detected only with cyclohexanol as substrate but not with the other alcohols. Although the enzyme utilizes both NADPH and NADH as cofactor, NADPH-dependent activity shows lower K m and V values for substrates than the NADH-dependent activity and the optimal pH is 4.8. The enzyme has higher affinity for NADPH than NADH and is inhibited more strongly by NADP + than by NAD + . The addition of NADPH or NADP + increases heat stability of the enzyme, but NADH and NAD + have no effect. The enzyme is uniquely inhibited by pyrazole as well as quercitrin, benzoate, SH-reagents, and reducing agents e.g., Fe 2+ , 2-mercaptoethanol, and dithiothreitol. Pyrazole is a noncompetitive inhibitor with K i values of 84 and 50 μ m with respect to both substrate and cofactor, respectively. The enzyme is electrophoretically and immunochemically different from the minor enzyme with low molecular weight, aldehyde reductase, purified from the same source. Thus, the enzyme is a novel pyrazole-sensitive carbonyl reductase.

Purification and characterization of pig lung carbonyl reductase

A pyrazole-sensitive carbonyl reductase from pig lung was purified to homogeneity by electrophoretic criteria. Chemical cross-linking study suggested that the native enzyme is a tetramer with a Mr of 103,000, consisting of apparent identical subunits of Mr 24,000. The enzyme reduced aliphatic and aromatic carbonyl compounds with NADPH as a preferable cofactor to NADH and catalyzed the oxidation of secondary alcohols and the aldehyde dismutation in the presence of NAD(P)+. Immunohistochemical study with the antibodies against the enzyme revealed that the enzyme was localized in the ciliated cells, nonciliated bronchiolar cells, Type II alveolar pneumocytes, and the epithelial cells of the ducts of the bronchial glands in the pig lung. In addition to the properties and distribution, the pig lung enzyme was immunochemically similar to the pulmonary enzymes in the guinea pig and mouse. However, the pig enzyme showed the following unusual features. (1) The enzyme exhibited an equatorial specificity in the reduction of 3-ketosteroids; the 4-pro-S hydrogen of NADPH was transferred to the carbonyl carbon atom of 5 alpha- and 5 beta-androstanes, and the respective reduced products were identified as 3 beta- and 3 alpha-hydroxysteroids. (2) Although the NADPH-linked reduction of carbonyl compounds apparently obeyed the Michaelis-Menten kinetics at pH 6.0, the double-reciprocal plots of the velocity vs concentrations of the carbonyl substrates were convex at pH higher than 6.5. The Hill coefficients and [S]0.5 values for the substrates decreased as the pH for reaction increased. The results suggest that the pig enzyme exhibits negative cooperativity with respect to the carbonyl substrates and that the hydrogen ion acts as an allosteric effector abolishing the negative interaction.

Isolation of multiple forms of indanol dehydrogenase associated with 17β-hydroxysteroid dehydrogenase activity from male rabbit liver☆

Seven multiforms of indanol dehydrogenase were isolated in a highly purified state from male rabbit liver cytosol. The enzymes were monomeric proteins with similar molecular weights of 30,000-37,000 but with distinct electrophoretic mobilities. All the enzymes oxidized alicyclic alcohols including benzene dihydrodiol and hydroxysteroids at different optimal pH, but showed clear differences in cofactor specificity, steroid specificity, and reversibility of the reaction. Two NADP+-dependent enzymes exhibited both 17 beta-hydroxysteroid dehydrogenase activity for 5 alpha-androstanes and 3 alpha-hydroxysteroid dehydrogenase activity for 5 beta-androstan-3 alpha-ol-17-one. Three of the other enzymes with dual cofactor specificity catalyzed predominantly 5 beta-androstane-3 alpha,17 beta-diol dehydrogenation. The reverse reaction rates of these five enzymes were low, whereas the other two enzymes, which had 3 alpha-hydroxysteroid dehydrogenase activity for 5 alpha-androstanes or 3(17)beta-hydroxysteroid dehydrogenase activity for 5 alpha-androstanes, highly reduced 3-ketosteroids and nonsteroidal aromatic carbonyl compounds with NADPH as a cofactor. All the enzymes exhibited Km values lower for the hydroxysteroids than for the alicyclic alcohols. The results of kinetic analyses with a mixture of 1-indanol and hydroxysteroids, pH and heat stability, and inhibitor sensitivity suggested strongly that, in the seven enzymes, both alicyclic alcohol dehydrogenase and hydroxysteroid dehydrogenase activities reside on a single enzyme protein. On the basis of these data, we suggest that indanol dehydrogenase exists in multiple forms in rabbit liver cytosol and may function in in vivo androgen metabolism.

Carbonyl reductase of dog liver: Purification, properties, and kinetic mechanism

A carbonyl reductase has been extracted into 0.5 M KCl from dog liver and purified to apparent homogeneity by a three-step procedure consisting of chromatography on CM-Sephadex, Matrex green A, and Sephadex G-100 in high-ionic-strength buffers. The enzyme is a dimer composed of two identical subunits of molecular weight 27,000. The pH optimum is 5.5 and the isoelectric point of the enzyme is 9.3. The enzyme reduces aromatic ketones and aldehydes; the aromatic ketones with adjacent medium alkyl chains are the best substrates. Quinones, ketosteroids, prostaglandins, and aliphatic carbonyl compounds are poor or inactive substrates for the enzyme. As a cofactor the enzyme utilizes NADPH, the pro-S hydrogen atom of which is transferred to the substrate. Two moles of NADPH bind to one mole of the enzyme molecule, causing a blue shift and enhancement of the cofactor fluorescence. The reductase reaction is reversible and the equilibrium constant determined at pH 7.0 is 12.8. Steady-state kinetic measurements in both directions suggest that the reaction proceeds through a di-iso ordered bi-bi mechanism.

Purification and characterization of purple acid phosphatase from rat bone.

An acid phosphatase, which was immunochemically identical to splenic purple acid phosphatase, was purified to homogeneity from rat bone. The enzyme was a two iron-containing monomeric glycoprotein with a mol. wt of 36,000. The enzyme hydrolyzed aryl phosphates, nucleoside di- and triphosphates, thiamine pyrophosphate, phosphoenolpyruvic acid and acidic phosphoproteins. The enzyme was inhibited by ammonium molybdate, NaF and CuSO4 but not by tartrate and SH-reagents.

Dihydrodiol dehydrogenases in guinea pig liver

Four major and four minor dihydrodiol dehydrogenases, with similar apparent molecular weights of 28,000 to 34,000 but with different charges, were purified from male guinea pig liver cytosol. One of the minor enzymes catalyzed only the oxidation of benzene dihydrodiol with a high Km value of 5.0 mM and was identified immunologically with aldehyde reductase. The other enzymes oxidized xenobiotic alicyclic alcohols and 17 beta-hydroxysteroids as well as benzene dihydrodiol. These enzymes exhibited higher affinity for 17 beta-hydroxysteroids than for alicyclic alcohols and benzene dihydrodiol, and immunologically cross-reacted with testosterone 17 beta-dehydrogenase purified from the same source. Four major enzymes and one minor with Km values for benzene dihydrodiol of about 0.2 mM, possessed specificity for 5 beta-androstane--17 beta-hydroxysteroids and dual cofactor requirement, whereas the other two minor enzymes with high Km values of over 5 mM showed apparent NADP and 5 alpha-androstane specificity. The dihydrodiol dehydrogenase activity was localized in the cytosol of liver. The results indicate that the hepatic oxidation of dihydrodiols in the guinea pig is mediated by cytosolic testosterone 17 beta-dehydrogenase isozymes and aldehyde reductase. Testosterone 17 beta-dehydrogenase immunologically identical to the liver enzymes was detected only in kidney, whereas aldehyde reductase was detected in all tissues of the guinea pig.

Aldehyde dismutation catalyzed by pulmonary carbonyl reductase : kinetic studies of chloral hydrate metabolism to trichloroacetic acid and trichloroethanol

The kinetics of the NAD(P)(+)-linked aldehyde dismutation by pulmonary carbonyl reductase of guinea pig were studied using a highly hydrated substrate, chloral hydrate (CH). The enzyme irreversibly converted the substrate into trichloroacetic acid (TCA) and trichloroethanol (TCE) in the presence of the reduced or oxidized cofactors, of which NAD(P)+ gave a higher reaction rate than did NAD(P)H, and the concentration ratios of the two products (TCA plus TCE) to CH utilized were 1:1. In the NAD(P)(+)-linked reaction TCA was the predominant product and its amount was compatible with that of TCE plus NAD(P)H produced, whereas in the NAD(P)H-linked reaction equal amounts of TCA and TCE were formed and the cofactor was little oxidized. These results suggest that the enzyme oxidized the hydrated aldehydes to TCA with NAD(P)+ as the cofactor and reduced the unhydrated aldehyde to TCE with NAD(P)H. The steady-state kinetic measurements in the NADP(+)-linked CH oxidation were consistent with an ordered Bi Bi mechanism which is the same as that for the secondary alcohol oxidation by the enzyme. The dehydrogenase activity was inhibited competitively with respect to CH by a secondary alcohol substrate, propan-2-ol. The CH and propan-2-ol dehydrogenase activities were similarly inactivated by 2,4,6-trinitrobenzene-sulfonate, and NADP(H), several cofactor analogs and a cofactor-competitive inhibitor, Cibacron blue dye, protected against the inactivation, which suggest that lysine residues are essential for catalysis.