Isocitrate lyase and malate synthase of Candida tropicalis grown on different carbon sources.

Abstract

The activities of isocitrate lyase and malate synthase-the key enzymes in the glyoxylate cycle-were found to be fairly high in n-alkane-, acetate-, and propionate-grown cells of Candida tropicalis compared with those in glucose-grown cells. In fact, the results of immunochemical studies showed that the increases in the enzyme levels resulted from increases in the amounts of the enzyme proteins. But the increases in these enzyme activities were not always coincident with the appearance of peroxisomes. Isocitrate lyase and malate synthase were purified from a peroxisome-containing particulate fraction of alkane-grown cells and from whole cells grown on glucose, acetate and propionate. The respective enzymes showed no significant differences in immunochemical properties, specific activities, molecular masses of active forms and subunits, on patterns of limited proteolysis with proteases, but the malate synthases of alkane- and propionate-grown cells showed higher Km values for acetyl-CoA than the enzymes of glucose- and acetate-grown cells. The results indicated that the synthesis of the key enzymes in the glyoxylate cycle did not necessarily have to be coincident with the development of peroxisomes in this yeast.