INFLUENCE OF ADDITIVES ON HIGH-PRESSURE STABILITY OF BETA-GALACTOSIDASE FROM KLUYVEROMYCES-LACTIS AND INVERTASE FROM SACCHAROMYCES-CEREVISIAE

High pressure denaturation of two yeast enzymes, Kluyveromyces lactis beta-galactosidase and Saccharomyces cerevisiae invertase in aqueous s olutions of salts and polyols was investigated. Polyols (more than sal ts) were shown to act as very effective agents against pressure denatu ration for both enzymes, lending to an increase in half-lives by facto rs between 1-10,000. NaBr and KBr were essentially destabilizing compo unds, leading to protective effects near zero in the case of beta-gala ctosidase. The maximum stability was obtained when KCl was used as add itive. The beta-galactosidase half-life is increased by a factor of 60 in a 3 M KCl solution and the invertase half-life by a factor of 40. Whereas NaCl had no stabilizing effect on beta-galactosidase lip to 2 M, this salt was of greater efficiency for invertase whatever the conc entration, leading to a protective effect of almost 30 at 3 M. The rue of polyols (glycerol, erythritol, xylitol, and sorbitol) allows beta- galactosidase and invertase to be stabilized against presence deactiva tion. This stabilizing effect increases with the polyol concentration, For invertase in the presence of xylitol, the half-life is increased by a factor of 7 at 1 M and by a factor near 50 at 2 M. The increase i n pressure resistance due to the presence of polyols was always greate r with beta-galactosidase than with invertase. The protective effect o f a 2 M xylitol solution is above 10,000 for beta-galactosidase wherea s it is about 50 for invertase. After the systematic study of the infl uence of salts and polyols, certain hypotheses are advanced on the pos sible mechanisms by which additives stabilize proteins to pressure den aturation. (C) 1998 Elsevier Science Inc.