Regulation of gluconeogenesis in the yeast Saccharomyces cerevisiae: Evidence for conversion of enolase isoenzymes

Regulation of gluconeogenesis is quite complex in S. cerevisiae . Two mechanisms have been described for controlling the level of gluconeogenic enzymes: carbon catabolite repression, another term is glucose repression, which preventes synthesis of certain enzymes; and carbon catabolite inactivation, which leads to destruction of gluconeogenic enzymes within 1 h after addition of glucose. Investigations ith antibodies have suggested a proteolytic process for inactivation. Inactivation of fructose-1, 6-bisphosphatase remained reversible for greater than or equal to 3 min after glucose addition. Whereas multiple forms of enolase were interpreted as the result from in vitro modification of the enzyme, 3 isoenzymes were demonstrated. Two of them were serologically identical, but without cross reaction with antibodies against the third enzyme. In the studies 3 isoenzymes, enolase I, enolase II and enolase III, were detected in cells growing with ethanol as carbon source, whereas only 2 isoenzymes were observed with glucose as carbon source. Addition of glucose to ethanol growing cells led to a rapid decrease in enolase I activity, whereas enolase II activity increased to the same extent. This indicated that enolase I was converted to enolase II under conditions of glucose repression.