[Citrate and glyoxylate cycle enzyme activity in citric and isocitric acid synthesis by different strains of Candida lipolytica]

Abstract

The activity of enzymes of the citrate and glyoxylate cycles was comparatively assayed in the parent strain of Candida lipolytica producing citric and isocitric acids in a medium with hexadecane and in its two mutants one of which produced citrate and the other synthesized isocitrate. The enzyme activities were determined in the dynamics of the yeast growth: (a) in the exponential growth phase (no production of the acids); (b) in the lag phase (the beginning of the acid production); and (c) in the stationary phase (active production of the acids). All of the strains had a high activity of citrate synthase. The mutant producing citrate exhibited a high activity of isocitrate lyase and a low activity of aconitate hydratase, whereas the mutant producing isocitrate manifested a high activity of aconitate hydrase and a low activity of isocitrate dehydrogenase and isocitrate lyase. The data pertinent to a change in the enzyme activities due to the growth limitation with a nitrogen source and the production of the acids are considered for explaining the mechanism of overproduction of citric and isocitric acids from n-alkanes by yeast organisms.