Role of asparaginase synthetase and asparagyl-transfer RNA synthetase in the cell-killing activity of asparaginase in Chinese hamster ovary cell mutants.

The cell-killing activity of asparaginase on three classes of Chinese hamster ovary cell mutants was examined: a mutant which overproduces asparagine synthetase (AH5); mutants defective in asparagine synthetase (N3 and N4); and mutants conditionally defective in asparagyl-transfer RNA synthetase (Asn 3, Asn 7, and Asn 9). The overproducer was more resistant to the cell-killing activity of asparaginase than wild-type Chinese hamster ovary cells, while mutants defective in asparagine synthetase were more sensitive. Surprisingly, the asparagyl-transfer RNA synthetase mutants were even more sensitive to asparaginase than the asparagine synthetase mutants. In a preliminary survey of four human lymphoid cell lines (RPMI 8402, RPMI 8392, B46M, and Molt-4F) which showed dramatically different asparaginase sensitivity, however, sensitivity to the cell-killing activity of asparaginase was correlated with reduced levels of asparagine synthetase and not with reduced levels of asparagyl-transfer RNA synthetase.