Immunochemical detection of human enzymes in hybrid cells

Rabbit antisera have been produced against each of three purified human enzymes: a cytoplasmic form of NADP-linked isocitrate dehydrogenase (IDH, EC 1.1.1.42), phosphoglucose isomerase (PGI, EC 5.3.1.9), and hypoxanthine guanine phosphoribosyltransferase (HGPRT, EC 2.4.2.8), and they have been used for immunoprecipitation reactions to detect human-specific enzymes in various human-mouse somatic cell hybrids. Under optimal conditions, enzyme activity was eliminated from human cell lysate, but no reduction of enzyme activity was found in the mouse cell lysate. Differential enzyme precipitation by these human-specific antisera was observed in human-mouse hybrid cells. Analysis on starch gel electrophoresis revealed that not only the human homodimer, but also human-mouse heterodimer molecules, in cases of PGI and IDH, were precipitated. Thus this method is sensitive and allows quantitative determination of human-specific enzymes. The presence of a human-specific enzyme identified by this method correlated with the presence of a particular human chromosome permitting assignments of the human cytoplasmic forms of NADP-linked IDH, human PGI, and human HGPRT genes to chromosomes 2, 19, and X, respectively. These assignments are consistent with published data (Ruddle, 1973).