Bieth J G, Tourbez-Perrin M, Pochon F
J Biol Chem. 1981 Aug 10;256(15):7954-7.
Soybean trypsin inhibitor, a protein of Mr = 20,000, has been used to assess the degree of inaccessibility of porcine trypsin within the alpha 2-macroglobulin-trypsin complex. The interaction between alpha 2-macroglobulin-bound trypsin and the inhibitor was demonstrated by affinity chromatography and trypsin inhibition. Whereas the free trypsin-inhibitor association is very fast (k = 1.2 X 10(7) M-1 s-1), the reaction between complexed trypsin and inhibitor takes 10 h to reach equilibrium. In addition, alpha 2-macroglobulin reduces, by several orders of magnitude, the affinity of trypsin for the inhibitor. Only one of the two trypsin molecules of the ternary (trypsin)2-alpha 2-macroglobulin complex is readily accessible to soybean inhibitor. It is postulated that the recently discovered proximity of the alpha 2-macroglobulin binding sites (Pochon, F., Favaudon, V., Tourbez-Perrin, M., and Bieth, J. (1981) J. Biol. Chem. 256, 547-550) accounts for this behavior. In the light of these results it is concluded that the proteinase binding sites are localized on the alpha 2-macroglobulin surface and that the two subunits of this protein are either not identical or not symmetrically arranged.
大豆胰蛋白酶抑制剂是一种分子量为20,000的蛋白质，已被用于评估α2-巨球蛋白-胰蛋白酶复合物中猪胰蛋白酶的不可及程度。通过亲和色谱法和胰蛋白酶抑制实验证明了α2-巨球蛋白结合的胰蛋白酶与抑制剂之间的相互作用。虽然游离胰蛋白酶与抑制剂的结合非常迅速（k = 1.2×10⁷ M⁻¹ s⁻¹），但复合胰蛋白酶与抑制剂之间的反应需要10小时才能达到平衡。此外，α2-巨球蛋白将胰蛋白酶对抑制剂的亲和力降低了几个数量级。在三元（胰蛋白酶）₂-α2-巨球蛋白复合物的两个胰蛋白酶分子中，只有一个容易被大豆抑制剂接近。据推测，最近发现的α2-巨球蛋白结合位点的接近性（Pochon, F., Favaudon, V., Tourbez-Perrin, M., and Bieth, J. (1981) J. Biol. Chem. 256, 547 - 550）可以解释这种行为。根据这些结果可以得出结论，蛋白酶结合位点位于α2-巨球蛋白表面，并且该蛋白质的两个亚基要么不相同，要么排列不对称。
