Biochemical activities during lipid accumulation inCandida curvata

Intracellular and extracellular concentrations of citrate and the specific activities of ten different enzymes in Candida curvata D were examined in relation to lipid biosynthesis in batch and continuous culture. Citrate was found to accumulate prior to lipid production and declined markedly as lipid accumulated in batch culture. The cells excreted citrate as the culture became nitrogen-limiting after 30 hr of growth, but little more was expelled after 40 hr when lipid accumulation was more marked. In continuous culture, only low levels of citrate were detected at the lower dilution rates and citrate was completely absent from both the cells and medium above a dilution rate of 0.1/hr. The activity of malic enzyme, malate dehydrogenase and ATP:citrate lyase increased in batch culture on lipid accumulated and, in continuous culture, both malic enzyme and ATP:citrate lyase varied in parallel with the specific rate of lipid synthesis which increased with increasing dilution rate. Activity of malate dehydrogenase, citrate synthase and glucose-6-phosphate dehydrogenase decreased with increasing dilution rate. The regulatory significance of these enzymes in lipid accumulation by C. curvata is discussed.