The Utilization of Pyruvic Acid by Bakers’ Yeast*

If sodium pyruvate is added to cells of bakers’ yeast suspended in a phosphate buffer of pH 7.0 in the strict absence of oxygen, practically no pyruvate is utilized. After 3 hours in contact with the cells the sodium pyruvate can be almost quantitatively recovered. If, however, oxygen is admiNed to the cells, then both pyruvate and oxygen are utilized at appreciable rates (see Table I). So far as I am aware, no one has pointed out this difference between aerobic and anaerobic conditions in connection with pyruvate metabolism by yeast, although one can infer from the literature that such must be the case. Thus Hagglund and Augustsson (1) and Haehn and Glaubitz (2) both remark that the utilization of pyruvate by yeast cells at neutrality is practically nil, whereas Lieben (3) measured a definite ut.ilization of sodium pyruvate by yeast cells while bubbling air through the suspension, and Meyerhof (4) obtained a comparatively large increase in oxygen consumption on adding sodium pyruvate to yeast cells. Such a marked difference between anaerobic and aerobic conditions is rather surprising, for, as is well known, yeast rontains an enzyme system, the carboxylase system, that rapidly attacks pyruvic acid under strict,ly anaerobic, as well as under aerobic condit,ions, according to the equation, CH&OCOOH + CH&HO + COz. This enzyme-catalyzed reaction occurs most rapidly at slightly acid reactions, so it might be considered that in experiments at neutrality this enzyme is inhibited. However,