Urea increases tolerance of yeast inorganic pyrophosphatase activity to ethanol: The other side of urea interaction with proteins

Ethanol is the major product of yeast sugar fermentation and yet, at certai n concentrations, it is very toxic to yeast cells. The major targets for et hanol's toxicity are the plasma membrane and the cytosolic enzymes: ethanol alters membrane organization and permeability and inactivates and unfolds globular cytosolic enzymes. The effects of ethanol on the plasma membrane a re attenuated by the presence of trehalose, a disaccharide of glucose that is accumulated simultaneously with urea. The data presented in this paper s how that trehalose is not effective at protecting yeast cytosolic inorganic pyrophosphatase against the inactivation of its catalytic activity promote d by alcohols. In contrast, 1 M trehalose increased the toxicity of alcohol s against pyrophosphatase by at least 34%. On the other hand, 1.5 M urea at tenuated the inactivation of pyrophosphatase promoted by alcohols by approx imately 50%. Here we propose that, in the presence of alcohols, urea functi ons as a molecular filter, enriching the vicinity of the protein with water and excluding alcohol molecules. Conversely, trehalose tends to increase t he interaction of alcohols with protein molecules, by withdrawing water, le ading to a stronger inactivation promoted for a given concentration of alco hol in the bulk solution on pyrophosphatase activity. (C) 2001 Academic Pre ss.