Human acylphosphatase cannot replace phosphoglycerate kinase in Saccharomyces cerevisiae

Human acylphosphatase (h-AP, EC 3.6.1.7) has been reported to catalyse the hydrolysis of the 1-phosphate group of 1,3-diphosphoglycerate. In vivo oper ation of this reaction in the yeast Saccharomyces cerevisiae would bypass p hosphoglycerate kinase and thus reduce the ATP yield from glycolysis. To in vestigate whether h-AP can indeed replace the S. cerevisiae phosphoglycerat e kinase, a multi-copy plasmid carrying the h-AP gene under control of the yeast TDH3 promoter was introduced into a pgk1 Delta mutant of S. cerevisia e. A strain carrying the expression vector without the h-AP cassette was us ed as a reference. For both strains, steady-state carbon- and energy-limite d chemostat cultures were obtained at a dilution rate of 0.10 h(-1)on a med ium containing a mixture of glucose and ethanol (15% and 85% on a carbon ba sis, respectively). Although the h-AP strain exhibited a high acylphosphata se activity in cell extracts, switching to glucose as sole carbon and energ y source resulted in a complete arrest of glucose consumption and growth. T he lack of a functional glycolytic pathway was further evident from the abs ence of ethanol formation in the presence of excess glucose in the culture. As h-AP cannot replace yeast phosphoglycerate kinase in vivo, the enzyme i s not a useful tool to modify the ATP yield of glycolysis in S. cerevisiae.