Kerfelec B, Chapus C, Puigserver A
Biochem Biophys Res Commun. 1984 May 31;121(1):162-7. doi: 10.1016/0006-291x(84)90701-0.
Reversible condensation of the ternary complex form of bovine pancreatic procarboxypeptidase A with 2,3-dimethyl maleic anhydride was investigated at pH 9.0 and low concentration of reagent over the acylable amino groups. After subsequent modification of only a few lysyl residues, subunit III was found to have been released from the quaternary structure leading to the separation of an apparently native protein devoid of any contaminating subunit II, while dissociation of the remaining binary complex occurred upon further addition of the anhydride. This observation suggests that the electrostatic interactions existing between subunits I and III are more rapidly weakened than those between subunits I and II, probably because fewer lysyl residues are involved and/or there is greater accessibility to the chemical reagent . Although completely inactive on the specific substrates of trypsin, chymotrypsin and elastase, subunit III hydrolyzed p-nitrophenyl acetate at a rate similar to that of chymotrypsin but without any burst of p-nitrophenol, which indicates that the weakly functional active site of the subunit is not quite comparable to that of serine protease zymogens. Subunit III already has some of the functional characteristics of the corresponding active enzymes.
在pH 9.0以及试剂浓度较低且酰化氨基存在的条件下，研究了牛胰羧肽酶原A的三元复合物形式与2,3 - 二甲基马来酸酐的可逆缩合反应。在仅对少数赖氨酰残基进行后续修饰后，发现亚基III从四级结构中释放出来，导致一种明显天然的、不含任何污染性亚基II的蛋白质分离出来，而在进一步添加酸酐后，剩余二元复合物发生解离。这一观察结果表明，亚基I和III之间存在的静电相互作用比亚基I和II之间的静电相互作用更快地减弱，这可能是因为涉及的赖氨酰残基较少和/或化学试剂更容易接近。尽管亚基III对胰蛋白酶、胰凝乳蛋白酶和弹性蛋白酶的特异性底物完全无活性，但它以与胰凝乳蛋白酶相似的速率水解对硝基苯乙酸，不过没有对硝基苯酚的任何快速释放，这表明该亚基的弱功能性活性位点与丝氨酸蛋白酶原的活性位点不太可比。亚基III已经具有相应活性酶的一些功能特性。
