Raae A J, Flengsrud R, Sletten K
University of Bergen Laboratory of Biotechnology, Bioblokken, Bergen, Norway.
Comp Biochem Physiol B Biochem Mol Biol. 1995 Oct;112(2):393-8. doi: 10.1016/0305-0491(95)00094-1.
Two chymotrypsin isoenzymes, ChT1 and ChT2 from cod pyloric caeca showed different kinetics against both chromogenic peptide and proteinaceous substrates. The enzymes have similar kcat values but ChT1 had substantially lower values for KM compared to ChT2. The enzymes also differed in cleaving site specificity with the oxidised B-chain of bovine insulin as substrate. ChT1 exhibited broader cleavage specificity compared to ChT2. This difference is parallel to the difference between chymotrypsin C and the A and B isotypes in higher animals. Direct N-terminal amino acid sequence analysis of the isoenzymes revealed that the active forms consisted of two polypeptide chains. The A chains were 13 residues long and ChT1 and ChT2 differed in three positions. The Cod enzyme A-chains differed from the A-chains of bovine chymotrypsin in four and five positions, respectively. The N-terminal part of the B-chains of the cod enzymes were nearly identical to that of the bovine A and B isoenzymes.
鳕鱼幽门盲囊中的两种胰凝乳蛋白酶同工酶ChT1和ChT2，对生色肽和蛋白质底物均表现出不同的动力学特性。这两种酶具有相似的kcat值，但与ChT2相比，ChT1的KM值要低得多。以牛胰岛素的氧化B链为底物时，这两种酶在切割位点特异性上也存在差异。与ChT2相比，ChT1表现出更广泛的切割特异性。这种差异与高等动物中胰凝乳蛋白酶C与A、B同种型之间的差异相似。对这些同工酶进行直接N端氨基酸序列分析表明，其活性形式由两条多肽链组成。A链长度为13个残基，ChT1和ChT2在三个位置上存在差异。鳕鱼酶的A链与牛胰凝乳蛋白酶的A链分别在四个和五个位置上不同。鳕鱼酶B链的N端部分与牛A、B同工酶的N端部分几乎相同。
