The optical rotation of ovalbumin changes with time in the presence of urea.The change does not follow a simple firstorder law. The half time of the change at 30°is inversely proportional to the fifteenth power of the urea concentration and depends only slightly on the ovalbumin concentration. The reaction is about one-tenth as fast at 20°as at either 0 or 40°. Among the other factors whose effects on the reaction have been studied are the following: hydrostatic pressure, pH, salts, detergents, sulfhydryl reagents, various organic substances, and changes of temperature and urea concentration during the reaction. The principal conclusions which can be drawn from the observations are these: (1) the change in optical rotation is caused by an intimate attack on the protein by the urea; the mere presence of urea in high concentration in the solvent around the protein does not affect the rotation. (2) The failure to give a first-order law is due either to the existence of a series of stages in the denaturation, or to the inhomogeneity of the native protein.(3) The action of urea is caused by complex formation between ovalbumin and urea rather than by a less localized, non-stoichiometric interaction of the solvent with the electric fields around the protein. ( 4) It is therefore theoretically justifiable to regard the denaturation of ovalbumin as a true fifteenth-order reaction with respect to urea at 0°. (5) The explanation given by Hopkins for the unusual temperature dependence of the rate can be given quantitative expression. The numerical values of the constants required by this analysis do not seem entirely reasonable if, as is usually assumed, urea acts by breaking hydrogen bonds within the protein. There may be a fundamental difference in the mechanisms of heat and urea denaturation. ( 6) Many processes in addition to the rupture of hydrogen bonds may control the rate of unfolding of ovalbumin in urea.observed that the optical rotations of proteins generally increase on denaturation by heat, urea,

No abstract

No abstract

No abstract

No abstract