Regulation of expression of liver-specific enzymes. III. Further analysis of a series of rat hepatoma X human somatic cell hybrids.

1. The expression of twelve liver-specific enzymes was analysed in twenty-one independent rat hepatoma X human somatic cell hybrids, and in some cases up to forty-one subclones were also tested. 2. Seventeen hybrids continued to express most of the rat liver-specific enzymes and in some cases human isozymes of glutamate-pyruvate transaminase, alpha-glycerophosphate dehydrogenase, guanine deaminase, alcohol dehydrogenase and pyruvate kinase were clearly identified. 3. Analysis of the segregation of the human liver-specific enzymes in these hybrids led to the assignment of human GPT to chromosome 8 (previously reported, Kielty, Povey & Hopkinson, 1982) and suggests the assignment of human GPD1 to chromosome 12. 4. The expression of the various liver-specific enzymes in these hybrids appeared to be controlled by independent regulatory mechanisms. 5. Four unusual reverse segregant hybrids were also analysed, and in these no liver-specific enzyme activity was demonstrable.