Summary auto-generated
De Deken describes the Crabtree effect, a regulatory system in Saccharomyces cerevisiae where high fermentation rates repress the synthesis of respiratory enzymes. When yeast grows exponentially on glucose or fructose with oxygen present, glucose degradation proceeds primarily via aerobic fermentation rather than respiration. However, on mannose or galactose, degradation occurs simultaneously through both pathways because their slower fermentation rates allow respiratory enzyme synthesis. This phenomenon represents repression of one energy-producing system (respiration) by another (fermentation). The author tested various yeast strains and found the Crabtree effect present in approximately 50% of them, though most Saccharomyces species exhibited it. Comparative analysis showed that organisms with the Crabtree effect have constitutive fermentation systems prioritizing fermentation over respiration, unlike Candida tropicalis which lacks the effect and uses fermentation primarily under anaerobic conditions. The growth-limiting factor during aerobic fermentation is energy production rate rather than availability of metabolic intermediates, suggesting the effect is controlled by cellular energy status rather than sugar metabolite accumulation.
Key findings
- The Crabtree effect is the repression of respiratory enzyme synthesis by high rates of aerobic fermentation in yeast growing on glucose or fructose
- When fermentation rates are low (mannose, galactose), respiratory enzymes are derepressed, allowing simultaneous respiration and fermentation that maintains normal growth rates
- Approximately 50% of tested yeast strains show the Crabtree effect, with most Saccharomyces species exhibiting it while organisms like Candida tropicalis do not
- The fermentation pathway is largely constitutive in Crabtree-positive strains, giving it priority over respiration as an energy source
- The repression is controlled by cellular energy status (ATP availability) rather than by accumulation of sugar degradation products
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Abstract
SUMMARY: When Saccharomyces cerevisiae is growing exponentially on glucose or fructose as carbon plus energy source, and in the presence of air, the glucose degradation proceeds mainly via aerobic fermentation. When the yeast is growing on mannose or galactose, degradation proceeds simultaneously via respiration and fermentation. This situation results from a repression of the of the respiratory enzymes synthesis by high fermentation rates. This regulatory system, called the “Crabtree effect”, consists actually of a repression of an energy source (respiration) by another energy source (fermentation). Various yeast strains were tested; the regulatory system was present in about 50% of them.