Extracts of brewer's yeast contain GABA which enhances activation of glycogen synthetase by insulin in isolated rat hepatocytes.

Extracts of brewer's yeast have been fractionated, and the effects of fractions on the incorporation of 14C-labelled precursors into glycogen by hepatocytes have been studied. Purification of fractions which enhanced response to insulin resulted in the isolation of gamma-aminobutyric acid (GABA) which stimulated glycogen synthetase activity in the presence but not in the absence of suboptimal insulin concentrations.