Mendoza-Hernández G, López-Solache I, Rendón J L
Departamento de Bioquímica, Facultad de Medicina, Universidad Nacional Autónoma de México, Mexico City.
Life Sci. 1990;47(5):467-75. doi: 10.1016/0024-3205(90)90306-c.
Activity of delta 5-3 beta-hydroxysteroid dehydrogenase coupled with steroid-delta 5-4-isomerase was demonstrated for the first time in the pancreas. The enzyme complex was assayed by measuring the conversion of pregnenolone to progesterone as well as of dehydroepiandrosterone to androstenedione and found to be localized primarily in the mitochondrial fraction of dog pancreas homogenates. The delta 5-3 beta-hydroxysteroid dehydrogenase used either NAD+ or NADP+ as co-substrates, although maximal activity was observed with NAD+. In phosphate buffer, pH 7.0 and 37 degrees C, the apparent Km values of the dehydrogenase were 6.54 +/- 0.7 microM for pregnenolone and 9.61 +/- 0.8 microM for NAD+. The apparent Vmax was determined as 0.82 +/- 0.02 nmol min-1 mg-1. Under the same conditions the Km values for dehydroepiandrosterone and NAD+ were 3.3 +/- 0.2 microM and 9.63 +/- 1.6 microM, respectively, and the apparent Vmax was 0.62 +/- 0.01 nmol min-1 mg-1.
δ5-3β-羟基类固醇脱氢酶与类固醇δ5-4-异构酶的活性首次在胰腺中得到证实。通过测量孕烯醇酮向孕酮以及脱氢表雄酮向雄烯二酮的转化来测定该酶复合物，发现其主要定位于犬胰腺匀浆的线粒体部分。δ5-3β-羟基类固醇脱氢酶以NAD⁺或NADP⁺作为共底物，尽管在NAD⁺存在时观察到最大活性。在pH 7.0和37℃的磷酸盐缓冲液中，该脱氢酶对孕烯醇酮的表观Km值为6.54±0.7μM，对NAD⁺为9.61±0.8μM。表观Vmax测定为0.82±0.02 nmol min⁻¹ mg⁻¹。在相同条件下，脱氢表雄酮和NAD⁺的Km值分别为3.3±0.2μM和9.63±1.6μM，表观Vmax为0.62±0.01 nmol min⁻¹ mg⁻¹。
