出版社：American Society for Biochemistry and Molecular Biology
摘要：The growth of Clostridium group P strain C48-50 [an anaerobe that contains 12alpha-hydroxysteroid dehydrogenase (12alpha-HSDH) in the absence of other dehydrogenases active upon bile salts] is greatly enhanced by the addition of 2.0% d-fructose or d-glucose to the growth medium. Other sugars were less effective. The production of NADP-dependent 12alpha-HSDH paralleled the growth of the organism which was optimal at 72 hr. Growth (and enzyme production) were suppressed by the addition of bile salt to the medium; the order of suppression was deoxycholate > chenodeoxycholate > cholate; 1 mM of either of the dihydroxy-bile salts inhibited 96% of the growth and 100% of the enzyme production. Kinetic studies on cell-free preparations of 12alpha-HSDH revealed a pH optimum of 7.8 with greater linearity of NADP evolution with time occurring only at more alkaline pH values (9-10). Lineweaver-Burke plots revealed Michaelis constant (K(m)) values in the range of 3-5 x 10(-4) M for deoxycholate and its glycine and taurine conjugates, while higher values were found for cholate and conjugates (K(m) value for taurocholate was 3 x 10(-3) M). Although there was no activity with NAD, 12alpha-HSDH was shown to bind onto both NAD- and NADP-Sepharose columns, with stronger binding on the latter. The enzyme was purified 20-fold by NAD-Sepharose chromatography. The molecular weight was estimated at 100,000 by Sephadex G-200 and a series of molecular weight markers. Substrate specificity studies showed that a variety of bile salts containing 12alpha-OH groups reacted; notably, the 3alpha-sulfates of cholate and deoxycholate were nonsubstrates.-Macdonald, I. A., J. F. Jellett and D. E. Mahony. 12alpha-Hydroxysteroid dehydrogenase from Clostridium Group P strain C48-50 #29733: partial purification and characterization.
