Unique Dihydrodiol Specific Dehydrogenase of Bovine Liver: Inhibition Studies and Comparison with Aldo/Keto Reductase

Abstract

Dihydrodiol dehydrogenase (EC 1.3.1.20: DD) catalyzes the dehydrogenation of the dihydrodiols of benzo(a)pyrene and benzo(a) anthracene in the presence of NADP⁺ and forms ortho-qninone (Vogel et al., 1980; Smithgall et al., 1988a). We previously reported on the purification of three multiple forms of bovine liver DD, DD1, DD2 and DD3, using benzenedihydrodiol Urcms-1,2-dihydrobenzene-1,2-diol) which is a model substrate for DD with NADP⁺ as a coenzyme (Nishinaka et al., 1991). DDl and DD2 have been identified with 3α-hydroxysteroid dehydrogenase (Nanjo et al., 1992) and high-ifm aldehyde reductase (Terada et al., 1985), respectively. On the other hand, DD3 is a unique enzyme which can specifically catalyze the dehydrogenation of benzenedihydrodiol and naphthalenedihydrodiol and has no activity toward other alcohols, aldehydes, ketones and quinones which are well known substrates for aldo/keto reductases. The Km-value of DD3 for benzenedihydrodiol was the lowest among the three enzymes. Thus, DD3, judging from its substrate specificity and inhibitor sensitivity, could not be classified into any known DD including carbonyl and aldehyde reductases and steroid dehydrogenases (Balcsak et al., 1983; Hara et al., 1986; Sawada et al., 1989). The most interesting property of DD3 is an immunological crossreactivity with DDl. Properties of bovine liver cytosolic DD were summarized in Table 1.