Arginine Biosynthesis by Streptococcus bovis1

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The pathway of arginine biosynthesis in Streptococcus bovis was studied by radioactive tracer techniques. Cells were grown anaerobically with 14CO2 in a synthetic medium containing NH4+ as the sole nitrogen source except for the trace present in nitrogen-containing vitamins. The protein fraction isolated from the labeled cells was acid-hydrolyzed, and 14C-arginine was isolated from the protein hydrolysate by ion-exchange chromatography. The carboxyl carbon of the isolated arginine was removed with arginine decarboxylase, and the guanidino carbon was removed by simultaneous arginase-urease degradation. By manometric measurement and liquid scintillation counting of the CO2 released by enzymatic degradation, 50% of the label was found in the carboxyl carbon and 50% in the guanidino carbon. Specific radioactivity determinations indicated that growth on 14CO2 resulted in twice as much label in arginine as with aspartate, glutamate, or lysine. These results are consistent with a glutamate → ornithine → citrulline pathway of arginine biosynthesis in S. bovis and provide further evidence for the synthesis of glutamate via the tricarboxylic acid cycle reactions from citrate through α-ketoglutarate.

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