Abstract
Four isozymes of 3α-hydroxysteroid dehydrogenase (3α-HSD) appeared in rat livers to be classified into three categories concerned with the requirement of coenzyme.
Two isozymes in the first group had affinity for both NAD and NADP. One of the other isozymes classified in the second was linked with NADP to show specificity for 5β-androstan-3α-ol-17-one (etiocholanolone) as the steroid substrate. An isozyme belonging to the third required only NAD as cofactor. This has the same migration rate of a lactate-dehydrogenase isozyme.
In the histochemical observation, the maximal activity of the enzyme was demonstrated with 5α-androstan-3α-ol-17-one (androsterone) but not with etiocholanolone as a substrate. On the other hand, all 3α-HSD isozymes revealed by electrophoresis showed a higher affinity for etiocholanolone than androsterone.
It is worthwhile to note that the zymogram of 3α-HSD in the cold acetone-treated section was essentially the same as the zymogram in the intact liver. All isozymes in the section were highest in activity when etiocholanolone was used as a substrate.
These findings indicate that in the cold acetone-treated section the enzyme still has affinity for etiocholanolone to resist the histochemical procedure employed.
