Dihydrofolate reductases from the wild type and aminopterin-resistant mutants of Diplococcus pneumoniae.

Dihydrofolate reductase from the wild type and aminopterin-resistant mutants of Diplococcus pneumoniae has been compared. Specific activity, optimum pH, Km, thermal stability, and inhibition by aminopterin are identical for both strains. Aminopterin resistance for such mutants is, therefore, not due to an alteration of the dihydrofolate reductase.