Federation proceedings 26 no. 388:page 736




Guinea pig brain cortex slices incubated in media containing U-C14 aspartic acid form glutamine of higher specific activity than glutamic acid (Fed. Proc. -25, 713 (1966) ). Glutamic acid and glutamine from such experiments were enzymatically decarboxylated and the o/o of label in C-1 ranged from 37 to 42o/o. These values exceed the maximum predicted from the known operation of the citric acid cycle viz. 33o/o. When l-C14 acetate was injected into mice or incubated with brain slices the aspartate isolated from brain had more than 50o/o of the label in C-4. From the known operation of the citric acid cycle it would be predicted that C -1 and C-4 should be equally labeled. The results of both series of experiments can be explained if it is assumed that the pyruvate moiety of oxaloacetate exchanges with unlabeled pyruvate from carbohydrate metabolism more readily than does the beta carboxyl group with COz. Supported by grants from NINDB and NIGMS.

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