By-product formation during exposure of respiring Saccharomyces cerevisiaecultures to excess glucose is not caused by a limited capacity of pyruvatecarboxylase

Upon exposure to excess glucose, respiring cultures of Saccharomyces cerevi siae produce substantial amounts of ethanol and acetate. A possible role of a limited anaplerotic capacity in this process was investigated by overexp ressing pyruvate carboxylase and by replacing it with a heterologous enzyme (Escherichia coli phosphoenolpyruvate carboxylase). Compared to the wild-t ype, neither the pyruvate carboxylase (Pyc)-overexpressing nor the transgen ic strain exhibited reduced by-product formation after glucose pulses to ae robic glucose-limited chemostat cultures. An increased intracellular malate concentration was observed in the two engineered strains. It is concluded that by-product formation in S. cerevisiae is not caused by a limited anapl erotic capacity. (C) 1999 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.