Stennicke H R, Mortensen U H, Breddam K
Carlsberg Laboratory, Department of Chemistry, Copenhagen, Denmark.
Biochemistry. 1996 Jun 4;35(22):7131-41. doi: 10.1021/bi952758e.
The activity of serine carboxypeptidases is dependent on a catalytic triad, an oxyanion hole, and a binding site equivalent to those found in the serine endopeptidases. The action of carboxypeptidase Y on substrates containing amino acids, alcohols, and amines as leaving groups is described. It is demonstrated that the features common to serine endopeptidases and carboxypeptidases are sufficient for hydrolysis of ester bonds. However, rapid hydrolysis of amide bonds is dependent on interactions between the C-terminal carboxylate group of the substrate and the C-terminal recognition site of the enzyme. Furthermore, on the basis of the pH dependencies of wild-type and mutant enzyme, combined with the ability of the enzyme to utilize binding energy to promote catalysis, alternative models for the high activity of carboxypeptidase Y at low pH are discussed. They describe how the catalytically essential histidine is maintained in its active deprotonated state through perturbation of its pKa value in the enzyme-substrate complex.
丝氨酸羧肽酶的活性依赖于一个催化三联体、一个氧负离子洞和一个与丝氨酸内肽酶中发现的那些相当的结合位点。描述了羧肽酶Y对含有氨基酸、醇和胺作为离去基团的底物的作用。结果表明，丝氨酸内肽酶和羧肽酶共有的特征足以实现酯键的水解。然而，酰胺键的快速水解依赖于底物的C端羧酸根基团与酶的C端识别位点之间的相互作用。此外，基于野生型和突变型酶的pH依赖性，结合酶利用结合能促进催化的能力，讨论了羧肽酶Y在低pH下高活性的替代模型。它们描述了催化必需的组氨酸如何通过酶-底物复合物中其pKa值的扰动而保持在其活性去质子化状态。
