Physiological properties of Saccharomyces cerevisiae from which hexokinaseII has been deleted

Hexokinase II is an enzyme central to glucose metabolism and glucose repres sion in the yeast Saccharomyces cerevisiae. Deletion of HXK2, the gene whic h encodes hexokinase II, dramatically changed the physiology of S. cerevisi ae. The hxk2-null mutant strain displayed fully oxidative growth at high gl ucose concentrations in early exponential batch cultures, resulting in an i nitial absence of fermentative products such as ethanol, a postponed and sh ortened diauxic shift, and higher biomass yields. Several intracellular cha nges were associated with the deletion of hexokinase II. The hxk2 mutant ha d a higher mitochondrial H+-ATPase activity and a lower pyruvate decarboxyl ase activity, which coincided with an intracellular accumulation of pyruvat e in the hxk2 mutant. The concentrations of adenine nucleotides, glucose-6- phosphate, and fructose-6-phosphate are comparable in the wild type and the hxk2 mutant. In contrast, the concentration of fructose-1,6-bisphosphate, an allosteric activator of pyruvate kinase, is clearly lower in the hxk2 mu tant than in the wild type. The results suggest a redirection of carbon flu x in the hxk2 mutant to the production of biomass as a consequence of reduc ed glucose repression.