Enzymes For Synthesis of 10-Formyltetrahydrofolate in Plants: Characterization of a Monofunctional 10-Formyltetrahydrofolate Synthetase and Copurification of 5,10-Methylenetetrahydrofolate Dehydrogenase and 5,10-Methenyltetrahydrofolate Cyclohydrolase Activities
Plants require folates for the biosynthesis of purines, serine, methionine, formylmethionyl-tRNA and thymidylate (1). In leaves, mitochondrial folates mediate glycine cleavage and serine formation during photorespiration (2). Plants also have enzymes (1,3) that interconvert methylene-and formyltetrahydrofolates. Alternatively, these species generate 10-HCO-H4PteGlu from formate (1). Recent work from Rabinowitz’s laboratory (4,5) on the latter reaction in spinach leaves, identified a monofunctional 10-HCO-H4PteGlu synthetase protein whose primary structure is like the synthetase domain of the mammalian and yeast trifunctional Cl-THF synthase. Partial purification of the related dehydrogenase and cyclohydrolase activities suggested they may occur as a bifunctional complex in spinach leaves (4). However, it is not clear whether this structural organization is typical of higher plants in general or may reflect a possible chloroplastic origin.
KeywordsSpinach Leave Streptomycin Sulphate Synthetase Protein High Plant Tissue Trifunctional Enzyme
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