Chih H. Wang

Carbon dioxide fixation and biosynthesis of amino acids in yeast

Abstract The time required for the label from 14 CO 2 to enter the various amino acids of yeast protein has been studied by means of paper chromatography and radioautography. Glutamic acid, aspartic acid and threonine become radioactive within the first 1 2 hour, emphasizing their rapid equilibrium with the primary products of 14 CO 2 fixation. Glycine and serine become radioactive by the end of the first hour and remain among the most radioactive of the amino acids throughout the period studied. This observation supports a previous proposal for the biosynthesis of these amino acids from a four carbon intermediate, which is probably one of the first formed carbon dioxide fixation products. Proline incorporates label very slowly and lysine not at all. These findings are in line with a slow turnover rate for proline and the known biosynthetic pathway for lysine. Valine labeling appearing before that in alanine suggests a decarboxylation-recarboxylation step in the formation of valine.