Conversion of acetate and pyruvate to aspartic acid in yeast.

Recent investigations by Ehrensviird et al. (1) have revealed that the carbon skeleton of aspartic acid in Torula yeast can arise readily from administered acetate. With C1aH&“OOH, the aspartic acid formed during growth contained Cl4 equally distributed between the two carboxyl groups, and most of the C** equally distributed between the 2 central carbon atoms. In the preceding papers (2, 3) the utilization of CH&lOOH and CH&L40COOH by bakers’ yeast has been compared, and have revealed that the incorporation of radioactivity into yeast protein is greater from pyruvate than from acetate. Although the major energy-yielding pathway of pyruvate metabolism appears to proceed through “active” acetate as an intermediate, points of divergence are known to exist in anabolic processes (4). The fixation of CO* or ita equivalent by pyruvate (5, 6) is one example. Since the extent to which pyruvate and acetate may follow a common pathway in t.he synthesis of yeast protein is unknown, the present study has been designed to establish this point: similar routes of metabolism would be reflected in similar patterns of distribution of activity in amino acids derived from carbonyl-labeled pyruvate and carboxyl-labeled acetate. The results described below indicate that, although aspartic acid from the acetate yeast bore the same C” distribution as that reported by Ehrensviird et al. (l), pyruvate produced a high degree of labeling in the amino carbon, suggesting that the Wood-We&man (5) or some similar reaction (6) was operative to a major extent.