The assimilation of 15NH3 by crude breis prepared from crushed soybean nodules was examined. The highest enrichment during 60 min of reaction time with 15N was found in alanine and the next highest in the amide-N of asparagine and glutamate. The labelling of allantoic acid was relatively low, although it was higher than that of other amino compounds. Nodule breis were separated into a bacteroid fraction and a supernatant plant fraction, and the 15NH3 incorporation into the main nitrogen compounds by each fraction was determined. The bacteroid fraction was much more efficient in converting 15NH3 into glutamate, alanine and glycine than the supernatant fraction, while for allantoic acid, the supernatant fraction showed a greater ability. The incorporation of 15NH3 into allantoic acid was strongly inhibited by the addition of azaserine or allopurinol, and enhanced by organic acid compounds, especially fumarate, succinate and malate. The mode of ureide formation in the course of ammonia assimilation in the soybean nodule is discussed.
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Fujihara et al. (1981) studied this question.