Metabolic responses of Saccharomyces cerevisiae CBS 8066 and Candida utilis CBS 621 upon transition from glucose limitation to glucose excess

Abstract

When chemostat cultures of Saccharomyces cerevisiae CBS 8066 and Candida utilis CBS 621, grown under glucose limitation, were pulsed with excess glucose, both organisms initially exhibited similar rates of glucose and oxygen consumption. However, striking differences were apparent between the two yeasts with respect to the production of cell mass in the culture and metabolite excretion. Upon transition from glucose limitation to glucose excess, S. cerevisiae produced much ethanol but the growth rate remained close to that under glucose limitation. C. utilis, on the other hand, produced little ethanol and immediately started to accumulate cell mass at a high rate. This high production rate of cell mass was probably due to synthesis of reserve material and not caused by a high rate of protein synthesis. Upon a glucose pulse both yeasts excreted pyruvate. In contrast to C. utilis, S. cerevisiae also excreted various tricarboxylic acid cycle intermediates, both under steady-state conditions and after exposure to glucose excess. These results and those of theoretical calculations on ATP flows support the hypothesis that the ethanol production as a consequence of pyruvate accumulation in S. cerevisiae, occurring upon transition from glucose limitation to glucose excess, is caused by a limited capacity of assimilatory pathways.

Localization and kinetics of pyruvate-metabolizing enzymes in relation to aerobic alcoholic fermentation in Saccharomyces cerevisiae CBS 8066 and Candida utilis CBS 621

“…This can be concluded from low extracellular pyruvate concentrations as reported by van Urk et al [5]. Assuming that the extracellular undissociated form of pyruvic acid is in equilibrium with the intracellular concentration, the intracellular pyruvate concentration can be calculated as follows:…”

“…Because the extracellular and intracellular pH (Fig. 5) and the extracellular pyruvate concentration (20-30 /~M for S. cerevisiae, see [5]) are known, the intracellular pyruvate concentration can be calculated to be 1-2 mM. This is below the K m values of the enzyme pyruvate decarboxylase ~or pyruvate at the high phosphate concentrations that are present in the cytosol (Fig.…”

“…This is likely to occur, since, after a glucose pulse, cells excreted pyrurate [5]. Apart from this, also the decrease in cytosolic phosphate concentration contributes to the activation of pyruvate decarboxylase after a glucose pulse, since the enzyme was inhibited by inorganic phosphate at physiological concentrations (Table V).…”

“…Upon transition from glucose limitation to glucose excess under aerobic conditions, the yeasts S. cerevisiae and C utilis show a different behaviour [4,5]: S. cerevisiae immediately starts to ferment (i.e., exhibits the short-term Crabtree effect [4]) whereas C utilis :loes not excrete fermentation products. Also the rate of accumulation of biomass is lfigher in cultures of C utilis [5].…”

A theoretical evaluation of growth yields of yeasts

“…Verduyn et al 1990a). Oxygen consumption and carbon dioxide production were determined and calculated according to van Urk et al (1988).…”