Deletion of the Glucose-6-Phosphate Dehydrogenase Gene Kl ZWF1 Affects both Fermentative and Respiratory Metabolism in Kluyveromyces lactis

Abstract

In Kluyveromyces lactis, the pentose phosphate pathway is an alternative route for the dissimilation of glucose. The first enzyme of the pathway is the glucose-6-phosphate dehydrogenase (G6PDH), encoded by KlZWF1. We isolated this gene and examined its role. Like ZWF1 of Saccharomyces cerevisiae, KlZWF1 was constitutively expressed, and its deletion led to increased sensitivity to hydrogen peroxide on glucose, but unlike the case for S. cerevisiae, the Klzwf1⌬ strain had a reduced biomass yield on fermentative carbon sources as well as on lactate and glycerol. In addition, the reduced yield on glucose was associated with low ethanol production and decreased oxygen consumption, indicating that this gene is required for both fermentation and respiration. On ethanol, however, the mutant showed an increased biomass yield. Moreover, on this substrate, wild-type cells showed an additional band of activity that might correspond to a dimeric form of G6PDH. The partial dimerization of the G6PDH tetramer on ethanol suggested the production of an NADPH excess that was negative for biomass yield.

The Yeast Genes ROX1, IXR1, SKY1 and Their Effect upon Enzymatic Activities Related to Oxidative Stress

“…Nevertheless, the protein does not seem to be essential, since mutants in its coding gene, ZWF1, can still grow in both respiratory and fermentative carbon sources (Nogae & Johston 1990;Saliola et al, 2007). The enzyme uses NADP + as a coenzyme, thus converting it to the reduced form NADPH, which is used by proteins with antioxidant functions.…”

Intracellular NADPH Levels Affect the Oligomeric State of the Glucose 6-Phosphate Dehydrogenase

“…No duplication of the KlZWF1 gene is present in the K. lactis genome, and a single mRNA transcript is expressed in wild-type cells grown in all carbon sources (33). Finally, both bands of activity disappear in Klzwf1⌬ mutants grown in ethanol (33). These data clearly indicate that both activity bands on the gel are from the KlZWF1 gene, the lower band probably originating from the upper one following changes in the oligomeric assembly.…”

“…The latter band was also present when ethanol was added to cultures growing in the above-mentioned carbon sources, indicating a dominant effect of this substrate over the others. The expression of the K. lactis gene in Saccharomyces cerevisiae showed the presence of five different migrating G6PDH bands of activity, suggesting a tetrameric organization of the enzyme (33). No duplication of the KlZWF1 gene is present in the K. lactis genome, and a single mRNA transcript is expressed in wild-type cells grown in all carbon sources (33).…”

“…The expression of the K. lactis gene in Saccharomyces cerevisiae showed the presence of five different migrating G6PDH bands of activity, suggesting a tetrameric organization of the enzyme (33). No duplication of the KlZWF1 gene is present in the K. lactis genome, and a single mRNA transcript is expressed in wild-type cells grown in all carbon sources (33). Finally, both bands of activity disappear in Klzwf1⌬ mutants grown in ethanol (33).…”

“…Recently, we characterized KlZWF1, the Kluyveromyces lactis gene coding for G6PDH, and showed that this enzymatic activity is required during growth on both respiratory and fermentative carbon sources (33). We developed an assay to detect on native polyacrylamide gels the G6PDH activity in cell extracts.…”