The temperature coefficient for the denaturation of chorionic and mare serum gonadotropins in aqueous and in urea solutions.

The denaturation of chorionic gonadotropin in 40 per cent aqueous urea solution has been found exceptional with respect to both the heat of activation and entropy of activation, but similar to other protein denaturations when compared on the basis of free energy of activation (1). The low rate (2) of inactivation of mare serum gonadotropin in 40 per cent aqueous urea solution at 37.5”, along with the above observation, prompted a study of the temperature coefficient for the inactivation of the mare serum hormone in 40 per cent aqueous urea solution. In the case of the chorionic gonadotropin, the inactivation was independent of concentration but the rate was such that a first order reaction could only be assumed on the basis that the reaction product was a stable substance with less biologic activity. The question arose concerning the free energy of the activation in the denaturation of chorionic gonadotropin compared with results for the mare serum hormone on the basis of total inactivation. The temperature coefficient for the inactivation of the reaction product of chorionic gonadotropin in 40 per cent aqueous urea solution was therefore determined and the original experiments were repeated with a hormone prepared by an entirely different procedure and of a higher degree of purity. A chorionic gonadotropin of E. R. Squibb and Sons was used; it had been prepared by tannic acid precipitation with subsequent fractionation, and assayed 300 I.U. per mg. in contrast to 100 I.U. per mg. for our original hormone. Finally, it seemed desirable to study the temperature coefficient for the inactivation of the two hormones in aqueous solution.