Compatibility of osmolytes with Gibbs energy of stabilization of proteins

This study led to the conclusion that naturally occurring osmolytes which a re known to protect proteins against denaturing stresses, do not perturb th e Gibbs energy of stabilization of proteins at 25 degrees C (Delta G(D)degr ees) which has been shown to control the in vivo rate of degradative protei n turnover (Pace et al., Acta Biol. Med. Germ 30 (1981) 1385-1392). This co nclusion has been reached from our studies of heat-induced denaturation of lysozyme, ribonuclease A, cytochrome c and myoglobin in the presence of dif ferent concentrations of osmolytes, namely, glycine, proline, sarcosine and glycine-betaine. At a fixed concentration of osmolyte a heat-induced denat uration curve measured by following changes in the molar absorption coeffic ient of the protein, was analyzed for T-m, the midpoint of the denaturation and Delta H-m, the enthalpy change of denaturation at T-m. Values of Delta G(D)degrees were determined with Gibbs-Helmoltz equation using known value s of T-m, Delta H-m, and Delta C-p, the constant-pressure heat capacity cha nge. It has been observed that T-m increases with the osmolyte concentratio n, whereas Delta G(D)degrees remains unaffected in the presence of the osmo lyte. This observation on Delta G(D)degrees in the presence of osmolytes ha s been considered in the physiological context. (C) 2000 Elsevier Science B .V. All rights reserved.