Isozyme patterns of branched-chain amino acid transaminase in cultured rat hepatocytes.

Abstract

Summary Three isozymes (Enzymes I to III) of branched-chain amino acid transaminase (EC 2.6.1.6) in various rat tissues and cultured hepatocytes were separated by diethylaminoethyl cellulose column chromatography and disc gel electrophoresis. It was found that normal liver contained Enzymes I and II, while normal brain and heart contained Enzymes III and I, respectively. Fetal liver contained Enzyme I only. It has been reported that poorly differentiated hepatomas contain Enzymes I and III. A pure clone of cultured rat hepatocytes contained only Enzyme I, but when the cells were transformed in vitro , either by 4-nitroquinoline 1-oxide or dimethylaminoazobenzene, Enzyme III appeared as well. Six of 12 cell strains isolated from the liver of newborn rats or adult rats that had been fed with chemical carcinogens contained Enzymes I and III, while the other six strains contained only Enzyme I. The chromosome numbers of the five strains with Enzymes I and III deviated markedly from the normal diploid pattern, while the other six strains showed less deviation. These results suggest that phenotypic expression of these isozymes is altered by genetic aberration and not by mere selection of a certain cell population.