The Amino Acid Composition and Distribution of N15 in Soybean Root Nodules Supplied N15-Enriched N2

Abstract

The amino acid composition of soybean root nodules was detd. by analysis of amino acid fractions separated by partition chromatography on starch columns. Arginine, ammonia, glutamic acid, lysine, and aspartic acid were the most abundant compounds. All of the common amino acids were present, and unidentified nin-hydrin positive compounds constituted but a small % of the total N. The amino acids separated from the soluble portion of nodules from soybean plants supplied N15-enriched N2 for 6 hrs. were analyzed for N15. The distr. of N15 was very similar to that observed in Azotobacter and Clostridium. The atom % N15 excess in glutamic acid was almost twice as high as that of any other amino acid and over 3 times as high as that of aspartic acid. These observations furnish further evidence that ammonia is the key intermediate in symbiotic N fixation.