The occurrence and properties of dihydrofolate reductase in pea seedlings |
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Authors: | SUZUKI, NOBORU IWAI, KAZUO |
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Affiliation: | Research Institute for Food Science, Kyoto University Kyoto, Japan |
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Abstract: | Dihydrofolate reductase (E.C. 1.5.1.3[EC]) was found in pea seedlingsand was partially purified by treatments with ammonium sulfate,protamine sulfate and by DEAE-cellulose column chromatography.Some properties of the enzyme were investigated. Optimum pHfor the reaction was 6.5. In the enzyme reaction, FAH2 and NADPH2were specifically required. MICHAELIS constants for FAH2 andNADPH2 were 4.3x106 M and 4.0x105 M, respectively.Folate antagonists such as aminopterin, methotrexate and pyrimethaminewere potent inhibitors of this enzyme. Enzyme activity was almostcompletely inhibited at a concentration of 107 M of aminopterinand methotrexate and 106 M of pyrimethamine. Growth of germinating pea seeds was inhibited by aminopterin,methotrexate and pyrimethamine, and it recovered significantlywith a tetrahydro-derivative of folate, CF, but not with dihydrofolicor folic acid. These results suggest that growth inhibitionof pea seedlings by these antagonists is due to inhibition ofdihydrofolate reductase in seedlings. 1Studies on the enzymatic synthesis and metabolism of folatecoenzymes in plants IV. (For the previous paper, Part III, seeReference (21)) . Part of this paper was presented at the AnnualMeeting of the Agricultural Chemical Society of Japan held atTokyo on April 4, 1967 (Received October 8, 1969; ) |
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