A new subunit of horse liver alcohol dehydrogenase and subunit composition of the polymorphic form

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Abstract
The most cathodal (on starch-gel electrophoresis), steroid-active band of horse liver alcohol dehydrogenase, whose catalytic properties were shown to be dependent on the livers used as a starting material was prepared from A-type and S-type horse livers by identical methods. Different isoenzymes are present in these preparations. Preparations from S-type livers consists of 1 component which has a subunit structure of SS (subunit S, active with steroids in addition to the classical substrates of alcohol dehydrogenase) and is identical with the SS isoenzyme described by Pietruszko and Theorell. Preparations from A-type livers consist of 3 components: one of these is the SS isoenzyme, the other 2 are previously unidentified isoenzymes of horse liver alcohol dehydrogenase. On the basis of the experimental evidence presented the preparations from A-type livers are composed of S and A subunits to form 3 isoenzymes: AA, AS and SS. Subunit A, a previously unidentified polypeptide, bears a catalytic site that does not catalyze interconversion of 3-oxo steroids or of 3.beta.-hydroxy steroids of A/B cis configuration. The A subunit, unlike the E and S subunits, occurs only in some horse livers and appears to be a polymorphic form of horse liver alcohol dehydrogenase.

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