Fukada H, Takahashi K, Sturtevant J M
Biochemistry. 1985 Sep 10;24(19):5109-15. doi: 10.1021/bi00340a023.
The binding of Streptomyces subtilisin inhibitor (SSI) to alpha-chymotrypsin (CT) (EC 3.4.21.1) was studied by isothermal and differential scanning calorimetry at pH 7.0. Thermodynamic quantities for the binding of SSI to the enzyme were derived as functions of temperature from binding constants (S. Matsumori, B. Tonomura, and K. Hiromi, private communication) and isothermal calorimetric experiments at 5-30 degrees C. At 25 degrees C, the values are delta G degrees b = -29.9 kJ mol-1, delta Hb = +18.7 (+/- 1.3) kJ mol-1, delta S degrees b = +0.16 kJ K-1 mol-1, and delta C p,b = -1.08 (+/- 0.11) kJ mol-1. The binding of SSI to CT is weak compared with its binding to subtilisin [Uehara, Y., Tonomura, B., & Hiromi, K. (1978) J. Biochem. (Tokyo) 84, 1195-1202; Takahashi, K., & Fukada, H. (1985) Biochemistry 24, 297-300]. This difference is due primarily to a less favorable enthalpy change in the formation of the complex with CT. The hydrophobic effect is presumably the major source of the entropy and heat capacity changes which accompany the binding process. The unfolding temperature of the complex is about 7 degrees C higher than that of the free enzyme. The enthalpy and the heat capacity changes for the unfolding of CT were found to be 814 kJ mol-1 and 17.3 kJ K-1 mol-1 at 49 degrees C. The same quantities for the unfolding of the SSI-CT complex are 1183 kJ mol-1 and 39.2 kJ K-1 mol-1 at 57 degrees C.
在pH 7.0条件下，采用等温滴定热分析法和差示扫描量热法研究了链霉菌枯草杆菌蛋白酶抑制剂（SSI）与α-胰凝乳蛋白酶（CT，EC 3.4.21.1）的结合。根据结合常数（S. Matsumori、B. Tonomura和K. Hiromi，私人通信）以及在5至30℃下进行的等温量热实验，得出了SSI与该酶结合的热力学量随温度的变化关系。在25℃时，相应数值为：ΔG°b = -29.9 kJ/mol，ΔHb = +18.7（±1.3）kJ/mol，ΔS°b = +0.16 kJ/(K·mol)，以及ΔCp,b = -1.08（±0.11）kJ/mol。与SSI和枯草杆菌蛋白酶的结合相比，SSI与CT的结合较弱[Uehara, Y., Tonomura, B., & Hiromi, K. (1978) J. Biochem. (Tokyo) 84, 1195 - 1202; Takahashi, K., & Fukada, H. (1985) Biochemistry 24, 297 - 300]。这种差异主要是由于与CT形成复合物时焓变更不利。疏水效应可能是结合过程中熵变和热容变化的主要来源。复合物的解折叠温度比游离酶高约7℃。在49℃时，CT解折叠的焓变和热容变化分别为814 kJ/mol和17.3 kJ/(K·mol)。在57℃时，SSI - CT复合物解折叠的相同量分别为1183 kJ/mol和39.2 kJ/(K·mol)。
