Studies on the Biochemical Synthesis of Asparagine

Abstract

Methods are described for the in vitro cultivation of the excised lupin embryo on a synthetic medium. The postulate that asparagine synthesis is not conditioned primarily by the presence of excess free ammonia and hence is not a detoxication mechanism has been experimentally confirmed in the lupin. Isolated embryos, when supplied with adequate carbohydrate and nitrogen in the medium, are unable to absorb and convert succinic, malic, pyruvic, lactic, and glyceric acids, and glycerol and succinmonamide to asparagine. Under similar conditions of carbohydrate and nitrogen supply fumaric, maleic, aspartic, exalacetic, and glutamic acids, and succindiamide are effective in stimulating the synthesis of asparagine. Of these compounds; glutamic adid is the most effective. Metabolic products of glutamic acid such as ketoglutaric, glutaric, and succinic acids are not effective. Combinations of glutamic acid with aspartic and oxalacetic acids in the absence of ammonia are likewise not effective in the stimulation of asparagine synthesis. An extract of embryo tissue is able to oxidize glutamic acid in the presence of boiled yeast juice. Amide formation has been demonstrated in such an extract to which was added glutamic and aspartic acids and ammonia. An attempt has been made to unify the above observations, and to explain the role of glutamate as an energy source in asparagine synthesis, with the energy transfer possibly taking place through the intermediation of a pyridine coenzyme. The unsatisfactory status of the postulated conversion of aspartic acid to asparagine has been pointed out and a scheme proposed to explain the introduction of energy into the system.