Kaplan J, Ray F A, Keogh E A
J Biol Chem. 1981 Aug 10;256(15):7705-7.
Rabbit alveolar macrophages exhibit high affinity surface receptors which recognize alpha 2-macroglobulin . protease complexes but not native alpha 2- macroglobulin. Binding of alpha 2-macroglobulin . protease complexes to surface receptors is independent of the protease used to form the complex. In this communication, we demonstrate that treatment of human alpha 2-macroglobulin with nucleophilic agents (methyl amine, ammonium salts) converts native alpha 2-macroglobulin into a form recognized by the surface receptor for alpha 2-macroglobulin protease complexes. Analysis of the concentration dependency of ligand binding revealed that the surface receptor did not distinguish between nucleophile-treated alpha 2-macroglobulin and alpha 2-macroglobulin . protease complexes. These results are consistent with the hypothesis that proteases or nucleophilic agents effect the hydrolysis of an internal thiol-ester bond (Tack, B. F., Harrison, R. A., Janatova, J., Thomas, M. L., and Prahl, J. W. (1980) Proc. Natl. Acad. Sci. U. S. A. 77, 5764-5768), leading to an alteration in alpha 2-macroglobulin conformation. The altered conformation results in recognition of the alpha 2-macroglobulin by surface receptors.
兔肺泡巨噬细胞表现出可识别α2-巨球蛋白-蛋白酶复合物而非天然α2-巨球蛋白的高亲和力表面受体。α2-巨球蛋白-蛋白酶复合物与表面受体的结合不依赖于用于形成复合物的蛋白酶。在本通讯中，我们证明用亲核试剂（甲胺、铵盐）处理人α2-巨球蛋白可将天然α2-巨球蛋白转化为一种能被α2-巨球蛋白-蛋白酶复合物的表面受体识别的形式。对配体结合浓度依赖性的分析表明，表面受体无法区分经亲核试剂处理的α2-巨球蛋白和α2-巨球蛋白-蛋白酶复合物。这些结果与蛋白酶或亲核试剂影响内部硫酯键水解的假说一致（塔克，B.F.，哈里森，R.A.，亚纳托娃，J.，托马斯，M.L.，普拉尔，J.W.（1980年）美国国家科学院院刊77，5764 - 5768），导致α2-巨球蛋白构象发生改变。构象改变使得α2-巨球蛋白能被表面受体识别。
