Ren X D, Dodds A W, Enghild J J, Chu C T, Law S K
Department of Biochemistry, University of Oxford, UK.
FEBS Lett. 1995 Jul 10;368(1):87-91. doi: 10.1016/0014-5793(95)00606-a.
The histidine at position 1106 of the C4B isotype of human complement is involved in catalyzing the covalent binding of the thioester to glycerol and water. By replacing the histidine with other residues, it was found that tyrosine is also capable of mediating the reaction. We propose that they act as nucleophiles by first attacking the thioester, upon activation, to form acyl intermediates, which subsequently react with the hydroxyl groups of glycerol or water. The monomeric alpha-macroglobulin, alpha 1I3 of the rat, was also studied. Unlike alpha 2-macroglobulin, which is a tetramer, alpha 1I3 has binding properties similar to those of C4A.
人类补体C4B同种型第1106位的组氨酸参与催化硫酯与甘油和水的共价结合。通过用其他残基取代组氨酸，发现酪氨酸也能够介导该反应。我们提出，它们在激活后首先攻击硫酯，作为亲核试剂形成酰基中间体，随后该中间体与甘油或水的羟基反应。还对大鼠的单体α-巨球蛋白α1I3进行了研究。与四聚体的α2-巨球蛋白不同，α1I3具有与C4A相似的结合特性。
