Quantitative analysis of the oxidative metabolism in HXK2- and REG1-deletion mutants of Saccharomyces cerevisiae

Abstract

Deletion mutants with either deletion of HXK2 and REG1 of the wild-type strain Saccharomyces cerevisiae CEN.PK113-7D were quantitatively analyzed for the impact on carbon catabolite repression and the short-term effect of the oxidative metabolism. Therefore, continuous cultures and transient experiments were performed, which were followed by high frequency on-line analysis of multiple compounds. It could be demonstrated that either deletion of HXK2 or REG1 alleviated repression of respiratory functions in steady state conditions. The most striking consequence of less repression was a constant level of the oxidative capacity in function of dilution rate in the oxido-reductive growth regime, which led to much higher biomass yields at dilution rates higher than D crit. Both mutants developed higher maximum oxidative capacity and consequently slightly higher critical dilution rate during steady state cultures. This finding suggests that also the maximum oxidative mitochondrial activity must be effected by carbon catabolite repression. The metabolic response to a sudden glucose excess, characterized by the instant availability of respiratory potential and the formation of ethanol, was not reduced by the deletion of HXK2 or REG1. However, the deletion mutants exerted a quicker adaptation of oxidative capacity to higher growth rates, which was attributed to the derepressed character of the deletion mutants. This relieved metabolic behavior led to a quicker return to oxidative catabolism after sudden glucose excess. This suggests that the short-term effect was not only dependent on the availability of the oxidative capacity, but also a consequence of metabolic coupling.