Thermal denaturation of human somatotropin, human choriomammotropin and ovine prolactin

The thermal denaturation of human choriomammotropin and ovine prolactin in 0.1 m tris-Cl buffer, pH 8.2, is a simple endothermic process which is at least partially reversible, and does not produce coagulation of the proteins. The transition temperatures suggest fairly stable conformations for these two proteins, but their enthalpies of denaturation are unusually low. The thermal denaturation of human somatotropin begins as an endothermic event with a considerably greater enthalpy of denaturation and a transition temperature higher than that of the other two hormones. However, before the endothermic portion of the denaturation can be completed, the human somatotropin coagulates, producing a powerful exothermic heat flow.