IN-SITU [C-14] GLUTAMATE METABOLISM BY DEVELOPING SOYBEAN COTYLEDONS .1. METABOLIC ROUTES

Glutamate metabolism was investigated in developing cotyledons of soybean (Glycine max (L.) Merrill). Intact excised cotyledons were injected with carrier-free C-14-glutamate and incubated, in the dark, in sealed vials containing a CO2 trap. Detection of C-14-radioactivity as released CO2, and ethanol-soluble and -insoluble fractions during 40-minute and 6-hour time courses, indicates that exogenously supplied glutamate was metabolized via CO2, 2-oxoglutarate, 4-aminobutyrate and Krebs-cycle intermediates. C-14-Labeled 4-aminobutyrate was recovered from the metabolism of [U-C-14]glutamate, but not [1-C-14]glutamate, demonstrating its production by decarboxylation of the carbon one of glutamate. The rapid metabolism of [C-14]4-aminobutyrate and the recovery of C-14-radioactivity in protein-aspartate suggest that glutamate decarboxylation is not a response to stress, but could contribute Krebs-cycle-derived amino acids for protein synthesis in co-operation with glutamate deamination and transamination. Recovery of C-14 as protein-arginine and -glutamate suggests that glutamate was also incorporated into arginine and protein, possibly without degradation. Multiple cellular amino acid pools were suggested from the rate of glutamate incorporation and the significant, but incomplete utilization of the soluble fraction.