Reversible Denaturation of Ribonuclease in Aqueous Solutions As Influenced by Polyhydric Alcohols and Some Other Additives

Abstract

Aqueous solutions of polyhydric alcohols protect the native conformation of ribonuclease against denaturation by heat, acid, and urea. The protective effect increases with the length of the molecule of the polyhydric alcohol and with its concentration. This stabilizing effect is explained in terms of a lessened hydrogen bond-rupturing capacity of the medium. Aqueous solutions of monovalent alcohols destabilize ribonuclease at high pH (high Tm) more than at low pH (low Tm). At elevated temperatures, at which it is principally hydrophobic bonds that determine the stability of the protein molecule, the interaction between hydrophobic molecules of the medium and the hydrophobic parts of the protein molecule is increased, resulting in a lessened stability of the protein molecule. Divalent alcohols destabilize ribonuclease to a much smaller degree than monovalent alcohols, when equimolar quantities of —CH2— and CH3— groups are present. This might be due to the fact that the interaction with water is increased by the second —OH group and hence the potency of the alcohol for weakening the hydrophobic bonds is decreased. The lowering in Tm of ribonuclease caused by urea is, in contrast to that caused by 1-propanol, counteracted by glycerol and sorbitol.