Role of phosphoenolpyruvate and 6-phosphogluconate in the short-term control of yeast isocitrate lyase

Phosphoenolpyruvate and 6-phosphogluconate inhibit yeast isocitrate lyase with different modes of action. Inhibition by 6-phosphogluconate is typically competitive and complete: that by phosphoenolpyruvate is noncompetitive and apparently partial, with some characteristics of an allosteric effect of V type. Analysis of the kinetic results—compared with the existing information about the inhibition of the enzyme from different organisms—suggests that in the yeast cell a short-term control of isocitrate lyase by phosphoenolpyruvate can be active, but perhaps plays only a partial role. In addition an isosteric feedback inhibition by 6-phosphogluconate can be present for the regulation of the glucogenetic pathway from acetyl-CoA, via the glyoxylate cycle.