Amino Acid Metabolism of Pea Leaves

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Abstract
Short term (2 h) incorporation of N from nitrate, glutamine or asparagine was studied by supplying them as unlabeled (14N) tracers to growing pea (Pisum sativum L.) leaves, which were previously labeled with 15N and then following the elimination of 15N from various amino components of the tissue. Most components had active and inactive pools. Ammonia produced from nitrate was assimilated through the amide group of glutamine. When glutamine was supplied, its N was rapidly transferred to glutamic acid, asparagine and other products, and there was some transfer to ammonia. N from asparagine was widely distributed into ammonia and amino compounds. There was a rapid direct transfer to glutamine, which did not appear to involve free ammonia. Alanine N was derived directly from asparagine, probably by transamination. Homoserine was synthesized in substantial amounts from all 3 N sources. Homoserine appears to derive N more readily from asparagine than from free aspartic acid. A large proportion of the pool of GABA turned over, and was replenished with N from all 3 supplied sources.