Characteristic Properties of Metabolism of the Yeast Yarrowia lipolytica during the Synthesis of α-Ketoglutaric Acid from Ethanol

The study of free amino acid content in Yarrowia lipolytica cells grown on ethanol under thiamine deficiency showed that glutamate, alanine, and gamma-aminobutyric acid (gamma-ABA) occurred in the highest concentrations among the present 17 free amino acids. The culture liquid contained no amino acids. Analysis of the enzymes of oxidative metabolism in the yeast grown under these conditions showed that the cell-free homogenate contained substantial activity of glutamate decarboxylase,gamma-ABA transaminase, and succinyl semialdehyde dehydrogenase. This result indicated the formation of succinate from glutamate in a reaction catalyzed by 4-aminobutyrate aminotransferase (gamma-aminobutyrate bypass) under severe thiamine deficiency. These studies lead to the conclusion that cultivation of the yeast Y. lipolytica on ethanol under thiamine deficiency causes adaptive stress-induced metabolic changes. Increase of ammonium nitrogen consumption and excretion of alpha-ketoglutaric acid are indicative of physiological changes, the functioning of the gamma-aminobutyrate bypass and high activity of malate dehydrogenase are manifestations of metabolic changes, and increased activities of the transamination reactions reflect the changes in nitrogen metabolism.