Alterations of the glucose metabolism in a triose phosphate isomerase-negative Saccharomyces cerevisiae mutant

The absence of triose phosphate isomerase activity causes an accumulation o f only one of the two trioses, dihydroxyacetone phosphate, and this produce s a shift in the final product of glucose catabolism from ethanol to glycer ol (Compagno et al., 1996), Alterations of glucose metabolism imposed by th e deletion of the TPI1 gene in Saccharomyces,cerevisiae were studied in bat ch and continuous cultures. The Delta tpi1 null mutant was unable to grow o n glucose as the sole carbon source. The addition of ethanol or acetate in media containing glucose, but also raffinose or galactose, relieved this ef fect in batch cultivation, suggesting that the Crabtree effect is not the p rimary cause for the mutant's impaired growth on glucose. The addition of a n energy source like formic acid restored glucose utilization, suggesting t hat a NADH/energy shortage in the Delta tpi1 mutant could be a cause of the impaired growth on glucose. The amount of glycerol production in the Delta tpi1 mutant could represent a good indicator of the fraction of carbon sou rce channelled through glycolysis. Data obtained in continuous cultures on mixed substrates indicated that different contributions of glycolysis and g luconeogenesis, as well as of the HMP pathway, to glucose utilization by th e Delta tpi1 mutant may occur in relation to the fraction of ethanol presen t in the media. Copyright (C) 2001 John Wiley & Sons, Ltd.