No abstract

No abstract

Thermodynamic parameters for the transition of native ribonuclease to the cross-linked random coil, induced by addition of guanidine hydrochloride, have been determined. The results are quite similar to those reported earlier for lysozyme.The effect of temperature can be described by assigning A H = 35 i 5 kcal/mole at 25", and ACp = 2200 + 500 cal/deg per mole, independent of temperature. The major part of the pH dependence of the equilibrium can be P revious papers from this laboratory (Aune and Tanford , 1969a,b, 1970) have reported the results of a study of the thermodynamics of the denaturation of lysozyme by guanidine hydrochloride (Gu . HC1). 1 It was found that the reaction involves only two states at 25", the native state (N) and the cross-linked random coil (D), which is the end product of denaturation by Gu.HC1. At higher temperatures a third discrete state, the heat-denatured state (X), was also found to contribute to the equilibrium properties. Below about 35" the results were interpreted entirely in terms of a single equilibrium constant KD, for the process N e D. It was found that KD could be written as a product of three independent functionsThe function F(aa) describes the dependence of KD on pH, and it was shown that it could be taken to be independent of the concentration of Gu.HC1 and of temperature, within the range over which these parameters were varied in the investigation. The function f(aG, .=c,) describes the dependence of KD on the activity of G u . HC1, and it was shown that it could be taken to be independent of pH and temperature. The parameter KDo is a function of temperature alone. It

No abstract