STUDIES ON WHEAT PLANTS USING C14COMPOUNDS: IV. DISTRIBUTION OF C14IN GLUTAMIC ACID, ASPARTIC ACID, AND THREONINE ARISING FROM ACETATE-1-C14AND -2-C14

Abstract

Glutamic acid, aspartic acid, and threonine isolated from the gluten of wheat plants to which acetate-1-C14or -2-C14was administered during growth have been degraded to determine the complete intramolecular distribution of C14. Sixty-three per cent of the activity in glutamic acid arising from acetate-1-C14was in carbon-5 and 20% in carbon-1; glutamic acid from acetate-2-C14contained 43% of the activity in carbon-4 and about 18% in each of carbons 2 and 3. Acetate-1-C14resulted in labelling largely in the terminal carbons of aspartic acid, and acetate-2-C14preferentially labelled the internal carbons. The results show that the Krebs' citric acid cycle provides a major pathway for the biosynthesis of the dicarboxylic amino acids of wheat gluten.Striking parallelism in the intramolecular distribution of carbon-14 in aspartic acid and threonine demonstrates that these amino acids are closely linked biosynthetically and is in accord with the idea that aspartic acid provides the carbon skeleton for threonine.