Oppezzo O, Ventura S, Bergman T, Vendrell J, Jörnvall H, Avilés F X
Institut de Biologia Fonamental, Universitat Autònoma de Barcelona, Spain.
Eur J Biochem. 1994 May 15;222(1):55-63. doi: 10.1111/j.1432-1033.1994.tb18841.x.
Three monomeric procarboxypeptidases and a binary complex consisting of a procarboxypeptidase and a chymotrypsinogen have been isolated from rat pancreas by HPLC. N-terminal sequence determination, substrate-specificity analysis and physico-chemical characterization showed that the carboxypeptidase precursors were the A1, A2 and B forms. No isomorphism could be detected for any of these proenzymes and no clear evidence was obtained for the presence of procarboxypeptidase-containing quaternary complexes of the types previously described for other species. Instead, we observed the presence of a binary complex between procarboxypeptidase A2 and chymotrypsinogen B. Among the major pancreatic endoproteinases, only trypsin was found to be a general activator of rat procarboxypeptidases in vitro. Time-course analysis of the products generated after trypsin addition confirmed that full activation of procarboxypeptidase A1 requires several cleavages in the C-terminal region (residues 87-94) of the activation segment, while procarboxypeptidases A2 and B require a single cleavage each. The carboxypeptidases released participate in the trimming of the activation segment in A1 and B, but not in A2, probably because of the high specificity of the latter in the active form.
通过高效液相色谱法（HPLC）从大鼠胰腺中分离出了三种单体羧肽酶原以及一种由羧肽酶原和胰凝乳蛋白酶原组成的二元复合物。N端序列测定、底物特异性分析和物理化学特性表征表明，这些羧肽酶前体分别为A1、A2和B型。未检测到这些酶原中的任何一种存在同构现象，也没有获得明确证据表明存在先前在其他物种中描述的那种含羧肽酶原的四级复合物。相反，我们观察到羧肽酶原A2和胰凝乳蛋白酶原B之间存在二元复合物。在主要的胰腺内蛋白酶中，仅发现胰蛋白酶在体外是大鼠羧肽酶原的通用激活剂。添加胰蛋白酶后对产生的产物进行的时间进程分析证实，羧肽酶原A1的完全激活需要在激活片段的C端区域（残基87 - 94）进行多次切割，而羧肽酶原A2和B各自只需单次切割。释放出的羧肽酶参与了A1和B中激活片段的修剪，但不参与A2中激活片段的修剪，这可能是因为后者在活性形式下具有高度特异性。
