Neutral lipid accumulation in yeast due to inositol deficiency: kinetic studies on the reciprocal regulation by fructose bisphosphate and citrate of yeast acetyl CoA carboxylase.

Neutral lipids, especially triacylglycerols, accumulated due to myo-inositol deficiency both in the cells of Saccharomyces carlsbergensis (Hayashi et al. (1976) J. Biol. Chem., 251, 5759--5769) and in the liver of the rat (Hayashi et al. (1974) Biochim. Biophys. Acta, 360, 134--155). The accumulation of triacylglycerols in the deficient yeast resulted, at least partly, from an enhancement of acetyl CoA carboxylase activity. The activation of the enzyme reflected the fluctuation due to the deficiency in the levels of fructose bisphosphate and citrate (Hayashi et al. (1978) Biochim. Biophys. Acta, 540, 231--237). Thus, the kinetics of the regulation of acetyl CoA carboxylase by these intermediates was studied. In physiological concentrations fructose bisphosphate sigmoidally activated acetyl CoA carboxylase from yeast with the Hill coefficient of 3, while citrate counteracted the fructose bisphosphate activation in a sigmoidal manner with the Hill coefficient of 2. Fructose bisphosphate markedly increased the apparent Vmax value of acetyl CoA carboxylase for the substrate, ATP and slightly decreased the apparent Km value. Citrate greatly decreased the apparent Vmax value increased by fructose bisphosphate.