Regulation of expression of liver-specific enzymes. II. Activation and chromosomal localization of soluble glutamate-pyruvate transaminase.

1. The expression of soluble GPT (E.C. 2. 6. 1. 2) was analysed in seventeen independent rat hepatoma/human somatic cell hybrids and in forty-one subclones derived from two of these hybrids. 2. As judged by electrophoretic mobility, twelve hybrid clones expressed rat GPT activity only and three expressed strong rat and weak human GPT activity but no heteromeric isozymes. In the remaining two hybrids, only human GPT was demonstrable. 3. The segregation of GPT and marker enzymes in the primary hybrid cells and the subclones suggests that the human structural GPT locus is on chromosome 8. 4. The re-expression of rat GPT in segregating subclones derived from two primary hybrids which had extinguished this function, could not be correlated with presence or absence of any particular human chromosome(s).