Formation of labelled amino acids by exchange transamination

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Abstract
In the presence of phosphoenolpyruvate, L-aspartate and an extract of Kalanchoe crenata, C14O2 has been introduced into the B-Carboxyl group of L-aspartate. The reaction is attributed to an initial carboxylation of phosphoenolpyruvate to yield oxaloacetate followed by an exchange transamination in which aspartate functions as the amino donor. The rate of accumulation of C14 in aspartate has been compared with that of the corresponding reaction, in which the initial carboxylation is followed by a normal transamination in which glutamate serves as the amino donor, and has been shown to be more rapid. The rate of the normal transamination between glutamate and oxaloacetate has been compared with that of the exchange transamination between glutamate and a-oxoglutarate in reactions catalyzed by an enzyme from Ricinus mitochondria. The results have been discussed in relation to their bearing on C14O2 feeding experiments.