Nature of Lactic Dehydrogenase Isozymes in Rat Kidney

Abstract

EVIDENCE has been published recently that lactic dehydrogenase (LDH) in most vertebrate tissues consists of two varieties combined as tetramers: the form of LDH predominant in heart tissue (H₄), the form predominant in muscle or liver (M₄), or hybrids of these (H₃M₁, and H₂M₂ and H₁M₃) (refs. 1, 2), The control of the relative percentages of these forms is believed to reside in two genes, one for the H form and one for the M form^1,2. In apparent contradiction to this theory, some tissues exhibit more than five LDH bands after electrophoretic separation^3,4. Electrophoresis of rat kidney homogenates yields six widely spaced bands. The extra isozyme (X-band) differs qualitatively from the other five in not requiring DPN or phenazine methosulphate (PMS) in the incubating medium for its demonstration. It apparently corresponds to a previously described band in rat kidney⁵, which also did not require DPN or PMS. The results of the experiments described below indicate that the additional X-isozyme is composed of a normal isozyme or hybrid the mobility of which is altered by migration in association with additional substances.