Sanchez-Ruiz J M, Lopez-Lacomba J L, Mateo P L, Vilanova M, Serra M A, Aviles F X
Departamento de Química-Física, Facultad de Ciencias, Universidad de Granada, Spain.
Eur J Biochem. 1988 Sep 1;176(1):225-30. doi: 10.1111/j.1432-1033.1988.tb14272.x.
Porcine pancreatic procarboxypeptidase A and its tryptic peptides, carboxypeptidase A and the activation segment, have been studied by high-sensitivity differential scanning calorimetry (DSC). The thermal denaturation of the zymogen and the active enzyme has been carried out at two pH values, 7.5 and 9.0, at different ionic strengths and at different scan rates. The endothermic transitions for these two proteins were always irreversible under all conditions investigated. The denaturation behaviour of both proteins seems to fit very well with the kinetic model for the DSC study of irreversible unfolding of proteins recently proposed by one of our groups. From this model, the activation energies obtained for the denaturation of the pro- and carboxypeptidase were 300 +/- 20 kJ mol-1 and 250 +/- 14 kJ mol-1 respectively. On the other hand, the isolated activation segment appears as a thermostable piece with a highly reversible thermal unfolding which follows a two-state process. The denaturation temperature observed for the isolated segment was always at least 15 K higher than those of the zymogen and the active enzyme.
利用高灵敏度差示扫描量热法（DSC）对猪胰羧肽酶原A及其胰蛋白酶消化肽、羧肽酶A和激活片段进行了研究。在两种pH值（7.5和9.0）、不同离子强度和不同扫描速率下对酶原和活性酶进行了热变性研究。在所有研究条件下，这两种蛋白质的吸热转变均为不可逆。这两种蛋白质的变性行为似乎与我们小组最近提出的蛋白质不可逆解折叠DSC研究动力学模型非常吻合。根据该模型，羧肽酶原和羧肽酶变性的活化能分别为300±20 kJ mol-1和250±14 kJ mol-1。另一方面，分离出的激活片段表现为一个热稳定片段，具有高度可逆的热解折叠过程，遵循双态过程。分离片段的变性温度总是比酶原和活性酶的变性温度至少高15K。
