Fioretti E, Angeletti M, Coletta M, Ascenzi P, Bolognesi M, Menegatti E, Rizzi M, Ascoli F
Department of Molecular, Cellular and Animal Biology, University of Camerino, MC, Italy.
J Enzyme Inhib. 1993;7(1):57-64. doi: 10.3109/14756369309020189.
The effect of pH and temperature on kinetic and thermodynamic parameters for the binding of the bovine basic pancreatic trypsin inhibitor (Kunitz inhibitor; BPTI) as well as bovine and porcine pancreatic secretory trypsin inhibitor (Kazal inhibitor; bovine and porcine PSTI, respectively) to human cathepsin G (EC 3.4.21.20) has been investigated. The affinity of the macromolecular inhibitors examined for cathepsin G is characterized by an endothermic, entropy-driven, behaviour, and shows the following trend: BPTI > bovine PSTI > porcine PSTI. The affinity difference of BPTI as well as of bovine and porcine PSTI for cathepsin G is mostly accounted for by changes in the values of the apparent dissociation rate constant for the proteinase:inhibitor complex destabilization. On increasing the pH from 4.5 to 9.5 (at 25.0 degrees C), the affinity of BPTI, as well as bovine and porcine PSTI for cathepsin G increases thus reflecting the acidic-pK shift of the His-57 catalytic residue from approximately 6.9 in the free enzyme to approximately 5.0 in the serine proteinase:inhibitor complexes. The BPTI as well as the bovine and porcine PSTI binding properties of cathepsin G have been analyzed in parallel with those of related serine (pro)enzyme/macromolecular inhibitor systems. Considering the known molecular models, the observed binding behaviour of BPTI as well as that of bovine and porcine PSTI to cathepsin G has been related to the inferred stereochemistry of the serine proteinase/inhibitor contact region(s).
研究了pH值和温度对牛碱性胰蛋白酶抑制剂（库尼兹抑制剂；BPTI）以及牛和猪胰分泌型胰蛋白酶抑制剂（卡扎尔抑制剂；分别为牛和猪PSTI）与人组织蛋白酶G（EC 3.4.21.20）结合的动力学和热力学参数的影响。所研究的大分子抑制剂对组织蛋白酶G的亲和力具有吸热、熵驱动的行为特征，并呈现以下趋势：BPTI＞牛PSTI＞猪PSTI。BPTI以及牛和猪PSTI对组织蛋白酶G的亲和力差异主要由蛋白酶-抑制剂复合物去稳定化的表观解离速率常数的变化所导致。在25.0℃下将pH值从4.5提高到9.5时，BPTI以及牛和猪PSTI对组织蛋白酶G的亲和力增加，这反映了His-57催化残基的酸性pK值从游离酶中的约6.9转变为丝氨酸蛋白酶-抑制剂复合物中的约5.0。已将组织蛋白酶G的BPTI以及牛和猪PSTI结合特性与相关丝氨酸（原）酶/大分子抑制剂系统的特性进行了平行分析。考虑到已知的分子模型，观察到的BPTI以及牛和猪PSTI与组织蛋白酶G的结合行为与推测的丝氨酸蛋白酶/抑制剂接触区域的立体化学有关。
