Entry of Glucose Carbon into Amino Acids of Rat Brain and Liver in Vivo after Injection of Uniformly 14-c-labelled Glucose.

1. Measurements were made of the rate of incorporation of (14)C from uniformly (14)C-labelled glucose into individual amino acids of rat brain and liver. 2. At 2.5 min. after intravenous injection of uniformly (14)C-labelled glucose, about 30% of the total radioactivity in the brain was present in the five amino acids studied. At 30 min. after subcutaneous injection the distribution of (14)C in amino acids was: in brain, alanine 2%, gamma-aminobutyrate 4%, aspartate 9%, glutamine 9% and glutamate 37% (total 69%); in liver, alanine 3%, aspartate 2.6%, glutamine 5.3% and glutamate 5.2% (total 18%). About 1% of the total radioactivity was in serine and glycine. 3. In both organs the specific radioactivity of alanine was initially higher than that of the other amino acids examined. The specific radioactivity of gamma-aminobutyrate in the brain was about the same as or higher than that of glutamate. 4. Amino acids of the rat brain were separated into ;free' and ;bound' fractions from brain dispersions in saline (or sucrose) media. Definite differences in the specific activities of the ;bound' and ;free' forms were not apparent.