Biochemical characterization of a mutant of the yeast Pichia anomala derepressed for malic acid utilization in the presence of glucose.

The mutant IGC 40 x 1001 of the yeast Pichia anomala IGC 4380, which displays inverse diauxic growth in a medium with glucose and malic acid, was studied to elucidate the biochemical mechanisms underlying that behavior. Time course changes of enzyme activities during growth of the mutant in that mixture of substrates indicated that the gluconeogenic enzymes remained active during the first phase of diauxic growth, while glycolytic enzyme activities were significantly reduced. This reduction was essentially due to an alteration in the maximum velocity and not in substrate affinity. Malate, citrate, and adenosine triphosphate did not affect significantly the activities of the glucose phosphorylating enzymes in cell extracts of either the mutant or the wild strain. In P. anomala, unlike Saccharomyces cerevisiae, the fructose/glucose phosphorylating ratio was not associated with repression/derepression conditions.