In a study of the role of methionine in protein chain initiation in wheat, a transformylase was isolated and partially purified from commercial wheat germ and from wheat leaves grown under sterile conditions. This enzyme catalyzed the formylation of a methionyl-tRNAf which was present in the wheat leaf chloroplasts. The enzyme used N10-formyltetrahydrofolate as formyl donor and required 5 mM Mg2+ and 20 mM K+ ions for maximum activity. The molecular weight of the transformylase was estimated at 45,000 by gel filtration on Sephadex G-150. The enzyme was present in isolated chloroplasts at a higher specific activity than in the remainder of the leaf extract. This transformylase and the methionyl-tRNAf are components of a protein chain initiating system in wheat chloroplasts similar in many ways to the system in Escherichia coli.
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