Properties and function of yeast pyruvate carboxylase.

Cannata and Stoppani (1, 2) found that bakers’ yeast contains an adenosine diphosphate-dependent phosphoenolpyruvate carboxykinase, and they ascribed the essential physiological role of oxaloacetate synthesis to it. Doubts concerning their interpretation arose, however, when it was revealed (3, 4) that cellfree preparations of the same microorganism could catalyze the direct carboxylation of pyruvate to oxaloacetate in the presence of adenosine triphosphate. Yeast pyruvate carboxylase was shown to be inhibited by oxalate and stimulated by either coenzyme A or its converted form, acetyl coenzyme A. Thus, yeast pyruvate carboxylase differs from the avian enzyme (5, 6), which depends absolutely on the presence of acetyl coenzyme A, and from the Aspergillus niger (7) and Pseudomonas citronellolis (8) enzymes, which do not have any requirement for this compound. The present paper describes a procedure for purification of pyruvate carboxylase from bakers’ yeast, and some of the properties of this enzyme, including its lability, affiity for various substrates, activators, and inhibitors, and the effect of PH. Attempts by Cannata and Stoppani (1) to demonstrate a malate enzyme in Saccharomyces cerevisiae have been unsuccessful. We have now found, however, as will be reported in this article, that the formation of this enzyme in another yeast, Rhodotorula glut&is, depends on the presence of malic acid or other related compounds in the growth medium. Blanchard, Korkes, Campillo, and Ochoa (9) have previously reported that an extremely active malate enzyme is present in Lactobacillus ar&inosus after culturing it in the presence of malic acid. Some of the experiments included in the present communication have been carried out in order to study the function of pyruvate carboxylase and related enzymes in both glycolysis and gluconeogenesis in yeast. For this purpose, two species have been grown on different carbon sources, and the specific activities of each enzyme have been estimated in the corresponding crude extracts. The results showed that pyruvate carboxylase varied only slightly, whereas pyruvate kinase, phosphoenolpyruvate carboxykinase, and malate enzyme drastically changed according to the carbon compound consumed by the yeast. The data obtained shed new light on the significance of these enzymes in several outstanding metabolic pathways.