Ascenzi P, Amiconi G, Bolognesi M, Onesti S, Petruzzelli R, Menegatti E
Department of Pharmaceutical Chemistry and Technology, University of Turin, Italy.
J Enzyme Inhib. 1991;5(3):207-13. doi: 10.3109/14756369109080059.
The effect of pH and temperature on the apparent association equilibrium constant (Ka) for the binding of the bovine and porcine pancreatic secretory trypsin inhibitor (Kazal-type inhibitor, PSTI) to human leukocyte elastase has been investigated. At pH 8.0, values of the apparent thermodynamic parameters for human leukocyte elastase: Kazal-type inhibitor complex formation are: bovine PSTI--Ka = 6.3 x 10(4) M-1, delta G degree = -26.9 kJ/mol, delta H degree = +11.7 kJ/mol, and delta S degree = +1.3 x 10(2) entropy units; porcine PSTI--Ka = 7.0 x 10(3) M-1, delta G degree = -21.5 kJ/mol, delta H degree = +13.0 kJ/mol, and delta S degree = +1.2 x 10(2) entropy units (values of Ka, delta G degree and delta S degree were obtained at 21.0 degrees C; values of delta H degree were temperature independent over the range (between 5.0 degrees C and 45.0 degrees C) explored). On increasing the pH from 4.5 to 9.5, values of Ka for bovine and porcine PSTI binding to human leukocyte elastase increase thus reflecting the acidic pK-shift of the His57 catalytic residue from congruent to 7.0, in the free enzyme, to congruent to 5.1, in the serine proteinase: inhibitor complexes. Thermodynamics of bovine and porcine PSTI binding to human leukocyte elastase has been analyzed in parallel with that of related serine (pro)enzyme/Kazal-type inhibitor systems. Considering the known molecular models, the observed binding behaviour of bovine and porcine PSTI to human leukocyte elastase was related to the inferred stereochemistry of the serine proteinase/inhibitor contact region(s).
研究了pH值和温度对牛和猪胰腺分泌型胰蛋白酶抑制剂（卡扎尔型抑制剂，PSTI）与人白细胞弹性蛋白酶结合的表观缔合平衡常数（Ka）的影响。在pH 8.0时，人白细胞弹性蛋白酶与卡扎尔型抑制剂形成复合物的表观热力学参数值如下：牛PSTI——Ka = 6.3×10⁴ M⁻¹，ΔG° = -26.9 kJ/mol，ΔH° = +11.7 kJ/mol，ΔS° = +1.3×10²熵单位；猪PSTI——Ka = 7.0×10³ M⁻¹，ΔG° = -21.5 kJ/mol，ΔH° = +13.0 kJ/mol，ΔS° = +1.2×10²熵单位（Ka、ΔG°和ΔS°的值是在21.0℃下获得的；ΔH°的值在所研究的温度范围（5.0℃至45.0℃之间）内与温度无关）。将pH值从4.5提高到9.5时，牛和猪PSTI与人白细胞弹性蛋白酶结合的Ka值增加，这反映了组氨酸57催化残基的酸性pK值从游离酶中的约7.0，转变为丝氨酸蛋白酶-抑制剂复合物中的约5.1。已将牛和猪PSTI与人白细胞弹性蛋白酶结合的热力学与相关丝氨酸（原）酶/卡扎尔型抑制剂系统的热力学进行了平行分析。考虑到已知的分子模型，观察到的牛和猪PSTI与人白细胞弹性蛋白酶的结合行为与推断的丝氨酸蛋白酶/抑制剂接触区域的立体化学有关。
