Novel Application of Glucagon and Insulin to Alter Yeast Glycogen Concentrations

Abstract

The glycogen content of brewers' yeasts has been used as an indicator of yeast vitality. Methods to artificially manipulate the yeast glycogen content rely on steps that could be expected to alter other cellular components. Consequently, an evaluation of the performance of such cells may not be directly related to glycogen concentrations. To alter only the cellular glycogen contents, we investigated the use of the hormones glucagon and insulin. Three different physiological conditions of yeast (aerobically grown, brewery fresh, and aged) were used. We found that both insulin and glucagon functioned as expected from their known activity in higher eucaryotes (mammals). Insulin promoted the conversion of glucose into glycogen. Glucagon stimulated glycogen breakdown and inhibited its synthesis at the end of fermentation. The effects of glucagon and insulin on glycogen level were enhanced in brewery-fresh yeast compared to aerobically grown yeast but minimal in aged yeast. It was postulated that diffusive movement of insulin and glucagon into the cell was eased in the case of yeast that actively divided. Increased membrane permeability also facilitated entry. These hormones may prove to be very useful metabolic tools to alter cellular glycogen concentrations without causing non-specific effects on commonly measured fermentation parameters.