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Plant and Cell Physiology, 1970, Vol. 11, No. 2 199-208
© 1970

Article

The occurrence and properties of dihydrofolate reductase in pea seedlings1

NOBORU SUZUKI and KAZUO IWAI

Research Institute for Food Science, Kyoto University Kyoto, Japan

Dihydrofolate reductase (E.C. 1.5.1.3 [EC] ) was found in pea seedlings and was partially purified by treatments with ammonium sulfate, protamine sulfate and by DEAE-cellulose column chromatography. Some properties of the enzyme were investigated. Optimum pH for the reaction was 6.5. In the enzyme reaction, FAH2 and NADPH2 were specifically required. MICHAELIS constants for FAH2 and NADPH2 were 4.3x10–6 M and 4.0x10–5 M, respectively. Folate antagonists such as aminopterin, methotrexate and pyrimethamine were potent inhibitors of this enzyme. Enzyme activity was almost completely inhibited at a concentration of 10–7 M of aminopterin and methotrexate and 10–6 M of pyrimethamine.

Growth of germinating pea seeds was inhibited by aminopterin, methotrexate and pyrimethamine, and it recovered significantly with a tetrahydro-derivative of folate, CF, but not with dihydrofolic or folic acid. These results suggest that growth inhibition of pea seedlings by these antagonists is due to inhibition of dihydrofolate reductase in seedlings.

1Studies on the enzymatic synthesis and metabolism of folate coenzymes in plants IV. (For the previous paper, Part III, see Reference (21)) . Part of this paper was presented at the Annual Meeting of the Agricultural Chemical Society of Japan held at Tokyo on April 4, 1967

(Received October 8, 1969; )
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