Zimmerman U J, Schlaepfer W W
Institute for Environmental Medicine, University of Pennsylvania Medical School, Philadelphia 19104.
Biochim Biophys Acta. 1991 Jun 24;1078(2):192-8. doi: 10.1016/0167-4838(91)99009-h.
Calcium-induced autolysis of bovine erythrocyte calpain I occurs in multiple stages. Initially, a 14 amino acid segment is cleaved from the N-terminus of the native 80 kDa catalytic subunit, yielding a 78 kDa form of the subunit. Then, an additional 12 amino acid segment is cleaved from the N-terminus, forming a 76 kDa subunit. The 76 kDa enzyme is the active form of the catalytic subunit that is able to proteolyze the 30 kDa regulatory subunit as well as exogenous substrates. While the initial autolytic step requires high calcium, the 76 kDa enzyme form is active in microM calcium and can cleave the amino termini of native 80 kDa and intermediate 78 kDa enzyme forms at low calcium. Both intramolecular and intermolecular proteolysis of the catalytic subunit appear to yield the same products.
钙诱导的牛红细胞钙蛋白酶I自溶分多个阶段发生。最初，从天然80 kDa催化亚基的N端切割掉一段14个氨基酸的片段，产生78 kDa形式的亚基。然后，再从N端切割掉一段12个氨基酸的片段，形成76 kDa亚基。76 kDa酶是催化亚基的活性形式，能够对30 kDa调节亚基以及外源底物进行蛋白水解。虽然最初的自溶步骤需要高钙，但76 kDa酶形式在微摩尔钙浓度下具有活性，并且在低钙条件下可以切割天然80 kDa和中间78 kDa酶形式的氨基末端。催化亚基的分子内和分子间蛋白水解似乎产生相同的产物。
