Isolation of a lactic dehydrogenase-A-deficient CHO-K1 mutant by nylon cloth replica plating.

A mutant Chinese hamster ovary cell deficient in lactate dehydrogenase A activity has been isolated using a nonselective technique. The method uses histochemical staining to examine colonies directly for enzyme activity and nylon cloth replica plating to recover particular clones. The mutant cell has an apparent Km (pyruvate to lactate) that is nearly tenfold higher than the parental cell, while its Vmax has been reduced more than 80-fold. In mutant cell extracts with added porcine LDH-B enzyme, molecular dissociation and recombination of subunits produces two new active LDH tetramers (A1B3, A2B2). The electrophoretic mobility of at least one of the tetramers (A1B3) was different from those formed in the parental extracts. The evidence suggests the variant cell contains a mutation in the structural gene for LDH-A.