Osterberg R, Pap S
Ann N Y Acad Sci. 1983;421:98-111. doi: 10.1111/j.1749-6632.1983.tb18096.x.
X-Ray scattering study of alpha 2-macroglobulin in solvents of variable electron densities (sucrose in water) shows that alpha 2-macroglobulin obeys the invariant volume hypothesis; thus, the structure of the particle is independent of the sucrose concentration of the solution. The particle structure is quantitatively described by a set of parameters such as the gyration radius, R = 8.0 nm, the volume, V = 1200 nm3, and the maximum distance within the particle, Dmax = 25 nm. The contrast dependence of the gyration radius indicates that in alpha 2-macroglobulin the regions of higher electron density are located closer to the center (core) than the regions of lower electron density. The core, which may be the place occupied by the carbohydrate, has a maximum dimension of 16 nm and it can be described as a flat cylinder. X-Ray scattering titrations indicate that alpha 2-macroglobulin forms a 1:2 complex as the main product with both trypsin and chymotrypsin simultaneously as the particle contracts. The formation of a ternary 1:1:1 complex with trypsin and chymotrypsin and the absence of higher complexes indicate that the sites for these proteases are closely related. This is further substantiated by the p(r) functions which are virtually identical for the 1:1:1 and 1:2 complexes.
在具有可变电子密度的溶剂（水中的蔗糖）中对α2-巨球蛋白进行的X射线散射研究表明，α2-巨球蛋白遵循不变体积假说；因此，颗粒的结构与溶液中蔗糖的浓度无关。颗粒结构通过一组参数进行定量描述，如回转半径R = 8.0 nm、体积V = 1200 nm3以及颗粒内的最大距离Dmax = 25 nm。回转半径的对比度依赖性表明，在α2-巨球蛋白中，较高电子密度区域比较低电子密度区域更靠近中心（核心）。核心可能是碳水化合物占据的位置，其最大尺寸为16 nm，可描述为扁平圆柱体。X射线散射滴定表明，随着颗粒收缩，α2-巨球蛋白与胰蛋白酶和胰凝乳蛋白酶同时形成1:2复合物作为主要产物。与胰蛋白酶和胰凝乳蛋白酶形成三元1:1:1复合物且不存在更高复合物表明，这些蛋白酶的作用位点密切相关。这通过1:1:1和1:2复合物的p(r)函数几乎相同得到进一步证实。
