Abstract
One major and six minor 17beta-hydroxy-C19-steroid dehydrogenases were isolated each in a highly pure form from male adult guinea pig liver by a combination of gel filtration and ion exchange chromatography. Molecular weight, amino acid composition, sugar content, number of sulfhydryl groups. NH2-terminal amino acid, isoelectric point, substrate specificity, pH optima, Km values, and inhibitory effect of other steroids were studied. The amino acid composition, Km values, and substrate specificity indicated two separate groups of enzymes. The first group possessed a dual coenzyme requirement and specificity for 5beta-androstanes, whereas the second group showed apparent TPN+ and 5alpha-androstane specificities. Phosphate enhanced the DPN+-related activity of the first group and evoked DPN+-linked activity in the second group of enzymes. A molecular weight of 31,000 to 32,000 with a single chain structure was estimated for four of the enzymes. The other three enzymes consisted of two components of 24,000 and 11,000 daltons.
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