Alteration in properties of thymidylate synthetase from pyrimethamine-resistant Plasmodium chabaudi

Abstract

Alteration in properties of thymidylate synthetase from pyrimethamine-resistant smodium chabaudi. International Journal for Parasitology 16: 483-490. Thymidylate synthetase from cloned strains of pyrimethamine-sensitive and resistant P. chubaudi were partially purified and characterized. The enzyme from both strains have equal mol. wt of 120,000 as estimated by Sephadex G-200 column chromatography. The enzyme from drug-sensitive parasites has an optimum pH of 6.5-7.5 and is stable at pH 4-11 while that from drug-resistant strain has an pH optimum of 7.0-8.0 and is stable at pH 5-10. The K m for methylenetetrahydrofolate are 206 ± 6 and 495 ± 5 μm for the enzyme from drug-resistant and sensitive parasites, respectively. The K m for dUMP of the enzyme from drug-resistant and sensitive parasites are 42 ± 1 and 49 ± 6 μm, respectively. Inhibition of the enzyme from both strains by FdUMP are competitive with dUMP; however,the K is for the enzyme from drug-resistant strain (0.043 ± 0.005 μm) is less than that from drug-sensitive strain (0.11 ± 0.007 μm) by a factor of 2.5. The K ii for methotrexate with respect to methylenetetrahydrofolate of the enzyme from drug-resistant parasites (58 ± 3 μm) is 3 times larger than that from drug-sensitive parasites (17 ± 1 μm). © 1986.