Isolation and characterization of glucose-6-phosphate dehydrogenase-deficient Chinese hamster cells derived from pure mutant colonies.

Ten pure glucose-6-phosphate dehydrogenase (G6PD)-deficient mutants were isolated from colonies composed entirely of cells which lacked G6PD staining activity. These mutants were analyzed for G6PD enzyme activity and the presence of immunologically cross-reactive proteins using immunoblotting techniques and antiserum directed against bovine G6PD. Four mutants had no detectable enzyme activity and did not contain protein which produces a detectable cross-reaction with G6PD antibody. One mutant had residual enzyme activity and altered electrophoretic mobility but did not have detectable immunological cross-reactivity. These results could be explained by either a DNA deletion or point mutational mechanism. On the other hand, five of the 10 mutants analyzed had characteristics consistent with a point mutation in the G6PD gene. All contain a protein which cross-reacts with the G6PD antibody and have the same subunit molecular weight as the parent cell's G6PD enzyme. Four of the five mutants had residual G6PD enzyme activity. Thus, the mechanism for the formation of pure mutants is not simply DNA deletion but is probably a more complex process involving the transfer of altered genetic information from one DNA strand to the other.