The pathway of hexose synthesis from pyruvate in muscle.

Although most of the reactions involved in the interconversion of glycogen and pyruvic acid are reversible, there is reason to believe that under physiological conditions the synthetic pathway may differ significantly from the degradativc (1, 2). In particular, the reaction catalyzed by phosphoenolpyruvate kinase, although reversible (3), contributes little to glycogen synthesis from pyruvate in liver or liver slices. It has been estimated that at least 90 per cent of pyruvate and lactat,e enters the “dicarboxylic acid shuttle” before incorporation int,o liver glycogen (4-6). Such data are consistent with pyruvate conversion t,o phosphopyruvat.e, and ultimately to hexose in liver via the reactions described by Ochoa et al. (7) and by Utter and Kurahashi (8):