MacDonald I A, Roach P D
Biochim Biophys Acta. 1981 Aug 24;665(2):262-9. doi: 10.1016/0005-2760(81)90011-4.
Eight strains of Clostridium absonum grown in the presence of 4 . 10(-4) M deoxycholate contained both NADP-dependent 7 alpha- and 7 beta-hydroxysteroid dehydrogenase activities. In one strain studied in detail, significant amounts of NADP-dependent 7 alpha- and 7 beta-hydroxysteroid dehydrogenase and NAD-dependent 7 alpha-hydroxysteroid dehydrogenase activities were demonstrated only when cells were grown in the presence of deoxycholate or chenodeoxycholate, both optimal at 4 . 10(-4) M. When the bile salt was deleted from the medium, only a trace of 7 alpha-hydroxysteroid dehydrogenase was present and 7 beta-hydroxysteroid dehydrogenase was absent. Other bile salts including cholate, ursodeoxycholate and keto bile salts were less effective as inducers. Addition of cholate to medium already containing deoxycholate at a suboptimal concentration enhanced the induction, while addition of ursodeoxycholate suppressed the induction. Further enhancement of 7 alpha- and 7 beta-hydroxysteroid dehydrogenase could be obtained by additions of deoxycholate (up to a total of 6 . 10(-4) M) during the growth of the organisms (in log phase). As enzyme enhancement is blocked by addition of rifampicin to the medium, the authors conclude that the enzymes are bile salt-inducible. Growth curve studies revealed an optimal enzyme yield at a harvest time of approx. 6-9 h. We have preliminarily characterized several inducible enzyme components: an NADP-dependent 7 beta-hydroxysteroid dehydrogenase as well as both NAD- and NADP-dependent 7 alpha-hydroxysteroid dehydrogenases.
在4×10⁻⁴ M脱氧胆酸盐存在的情况下培养的8株奇异梭菌，同时含有NADP依赖性7α-和7β-羟基类固醇脱氢酶活性。在对其中一株进行详细研究时发现，只有当细胞在脱氧胆酸盐或鹅去氧胆酸盐存在的情况下生长时，才会表现出大量的NADP依赖性7α-和7β-羟基类固醇脱氢酶以及NAD依赖性7α-羟基类固醇脱氢酶活性，二者在4×10⁻⁴ M时诱导效果最佳。当培养基中去除胆盐时，仅存在微量的7α-羟基类固醇脱氢酶，而7β-羟基类固醇脱氢酶则不存在。包括胆酸盐、熊去氧胆酸盐和酮胆盐在内的其他胆盐作为诱导剂的效果较差。向已经含有次优浓度脱氧胆酸盐的培养基中添加胆酸盐可增强诱导作用，而添加熊去氧胆酸盐则会抑制诱导作用。在生物体生长（对数期）期间添加脱氧胆酸盐（总量可达6×10⁻⁴ M），可进一步增强7α-和7β-羟基类固醇脱氢酶的活性。由于向培养基中添加利福平会阻断酶活性的增强，因此作者得出结论，这些酶是胆盐诱导型的。生长曲线研究表明，在收获时间约为6 - 9小时时酶产量最佳。我们已经初步鉴定了几种可诱导的酶成分：一种NADP依赖性7β-羟基类固醇脱氢酶以及NAD依赖性和NADP依赖性7α-羟基类固醇脱氢酶。
