THE OCCURRENCE AND PROPERTIES OF METHYLENE-TETRAHYDROFOLATE DEHYDROGENASE IN PEA SEEDLINGS, AND INTRACELLULAR DISTRIBU-TION OF SOME FOLATE-LINKED ENZYMES IN THE PLANT
1974 Volume 20 Issue 2 Pages 89-96
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1974 Volume 20 Issue 2 Pages 89-96
Methylenetetrahydrofolate dehydrogenase (EC 1.5.1.5) which is responsible for the enzymatic convertion of 5, 10-methylene-H4FA to 5, 10-methenyl-H4FA was found in various plant tissues. The enzyme was partially purified from pea seedlings and some of its properties were investigated. The enzyme was purified about 40-fold by fractionation with ammonium sulfate and gel-filtration. The optimum pH was 7.8. 5, 10-Methylene-H4FA and NADP were specifically required in the enzymatic reaction. Their Km values were 3.5×10-4M and 5.1×10-5M, respectively. Intracellular distribution of some folate-linked enzymes, i.e., methylenetetrahydrofolate dehydrogenase, formyltetrahydrofolate synthetase, methenyltetrahydrofolate cyclohydrolase, and phosphoribosylaminoimidazolecarboxamide formyltransferase, in pea seedlings were investigated. Major portions of these enzymes were located in the soluble fraction, while some activities of these enzymes were significantly detected in mitochondrial or microsomal fraction. A possible pathway for the synthesis and metabolism of folate coenzymes in plants is discussed.
