A potential role of the cytoskeleton of Saccharomyces cerevisiae in a functional organization of glycolytic enzymes.

Numerous individual enzymes participate in a given synthetic or degradative pathway in which the product of one reaction becomes the substrate for the subsequent enzyme. This raises the question of whether the product of one 'soluble' enzyme diffuses freely through the available cell volume, where it accidentally collides with the subsequent 'soluble' enzyme. Alternatively, enzymes acting in a given pathway may be organized in ordered structures, metabolons. Certain glycolytic enzymes have been shown to co-localize with the cytoskeleton in mammalian cells. We deleted genes coding for proteins associated with the cytoskeleton of Saccharomyces cerevisiae: TPM1 coding for tropomyosin, SAC6 for fimbrin and CIN1 for a microtubule-associated protein. Single deletions or deletions of two such genes had no effect on the specific activities of glycolytic enzymes, or on the rates of glucose consumption and ethanol production. However, the concentrations of glycolytic metabolites during a switch from a gluconeogenic mode of metabolism, growth on an ethanol medium, to glycolysis after glucose addition showed transient deviations from the normal change in metabolite concentrations, as observed in wild type cells. However, all metabolites in mutant strains reached wild-type levels within 2-4 h after the shift. Only ATP levels remained low in all but the tmp1-Delta-sac6-Delta double mutant strains. These observations can be interpreted to mean that metabolic reorganization from a gluconeogenic to a glycolytic metabolism is facilitated by an intact cytoskeleton in yeast.