Hylemon P B, Sherrod J A
J Bacteriol. 1975 May;122(2):418-24. doi: 10.1128/jb.122.2.418-424.1975.
Multiple forms of 7-alpha-hydroxysteroid dehydrogenase were detected in six of nine strains of Bacteroides fragilis. The enzymes differed with respect to pyridine nucleotide specificity, thermal stability, divalent metal cation requirement, and elution profilies from Sephadex G-200 columns. The nicotinamide adenine dinucleotide phosphate (NADP)-dependent enzyme required divalent metal cations, preferentially Mn-2+ (Km, 57 muM), for maximum catalytic activity. The NADP-dependent enzyme was labile at 65 C for 10 min, whereas the nicotinamide adenine dinucleotide (NAD)-dependent enzyme was stable at 65 C for 10 min. The specific activity of both the NAD- and NADP-dependent enzymes in crude extracts increased markedly (15- and 7.5-fold, respectively) during the transition from exponential- to stationary-phase growth in glucose medium containing 0.5 mM sodium cholate. The time course of apparent enzyme induction correlated temporally with the transformation of the 7-alpha-hydroxy group of cholate in the culture supernatant fluid. Both NAD- and NADP-dependent 7-alpha-hydroxysteroid dehydrogenase activities were found to be widely, but not universally, distributed in different strains and subspecies of B. fragilis. No NAD- or NADP-dependent 7-alpha-hydroxysteroid dehydrogenase activity could be detected in B. fragilis subsp. vulgatus Virginia Polytechnic Institute (VPI) no. 4245, subsp. thetaiotaomicron VPI 0061-1, or subsp. distasonis VPI 4243.
在9株脆弱拟杆菌中，有6株检测到了多种形式的7-α-羟基类固醇脱氢酶。这些酶在吡啶核苷酸特异性、热稳定性、二价金属阳离子需求以及从葡聚糖G-200柱上的洗脱图谱方面存在差异。烟酰胺腺嘌呤二核苷酸磷酸（NADP）依赖性酶需要二价金属阳离子，优先是Mn-2 +（Km，57μM），以实现最大催化活性。NADP依赖性酶在65℃下10分钟不稳定，而烟酰胺腺嘌呤二核苷酸（NAD）依赖性酶在65℃下10分钟稳定。在含有0.5 mM胆酸钠的葡萄糖培养基中，从指数生长期过渡到稳定期生长期间，粗提物中NAD和NADP依赖性酶的比活性均显著增加（分别增加15倍和7.5倍）。表观酶诱导的时间进程在时间上与培养上清液中胆酸盐7-α-羟基的转化相关。发现NAD和NADP依赖性7-α-羟基类固醇脱氢酶活性在脆弱拟杆菌的不同菌株和亚种中广泛但并非普遍分布。在脆弱拟杆菌亚种vulgatus弗吉尼亚理工学院（VPI）4245号、亚种thetaiotaomicron VPI 0061-1或亚种distasonis VPI 4243中未检测到NAD或NADP依赖性7-α-羟基类固醇脱氢酶活性。
