FOLATE REDUCTASE AND SPECIFIC DIHYDROFOLATE REDUCTASE OF AMETHOPTERIN-SENSITIVE STREPTOCOCCUS FAECIUM VAR DURANS

The dihydrofolate reductase activity of the folate-dependent, amethopterin-sensitive strain of Streptococcus faecium var. durans (SF/O) has been separated into two components that differ inseveral properties. The major component is a highly active specific dihydrofolate reductase; it hasbeen purified 400-fold with an over-all recovery of 33%. The minor component, which has a 9-fold lower turnover number in dihydrofolate reduction, catalyzes the reduction of folate also. Designated,therefore, folate reductase, it has been purified 40-fold with 25% yield. Structurally theseenzymes differ. The more basic protein, specific dihydrofolate reductase, migrates during molecular sieve chromatography as if its molecular weight were 3000 less than that of folate reductase. Theestimated molecular weight (19,000) of folate reductase resembles that of animal reductaseswhich catalyze the reduction of folate and dihydrofolate. Properties of folate reductase identify itas the enzyme which is the prevailing form of dihydrofolate reductase in the amethopterinresistant mutant strain, S. faecium var. durans/Ak. Positive induction by exogenous folate of onlythe specific dihydrofolate reductase has been observed. © 1969, American Chemical Society. All rights reserved.