Bergsma J, Vije J, Duursma A M, Schutter W G, Bouma J M, Gruber M
Biomed Biochim Acta. 1986;45(11-12):1549-56.
Rat alpha 2M was isolated from plasma of animals which had been treated with stress hormones. Polyacrylamide-gel electrophoresis of the reduced protein in the presence of sodium dodecyl sulfate showed a band with a Mr of 175,000. In a previous work (Biochem. J. 226, 75-84, 1985) we had found that rat alpha 1M consists of two types of subunits with Mr's of 163,000 and 37,000. Like the large subunit of alpha 1M the chain of alpha 2M contained a peptide bond that was susceptible to autolysis and a site that was split by trypsin. Negatively stained free alpha 2M could be distinguished from free alpha 1M under the electron microscope. Radioactively labelled alpha 2M was slowly cleared from plasma, but complexes of the protein with labelled subtilisin were rapidly cleared with first-order kinetics, showing a half-life of about 6 min. These complexes were mainly taken up by the liver, as had previously been described for alpha 1M-subtilisin complexes. Complexes of both macroglobulins competed with each other for uptake, indicating endocytosis via a common receptor.
大鼠α2M是从经应激激素处理的动物血浆中分离出来的。在十二烷基硫酸钠存在下对还原蛋白进行聚丙烯酰胺凝胶电泳，显示出一条Mr为175,000的条带。在先前的一项研究（《生物化学杂志》226, 75 - 84, 1985）中，我们发现大鼠α1M由两种亚基组成，其Mr分别为163,000和37,000。与α1M的大亚基一样，α2M的链含有一个易被自溶的肽键和一个被胰蛋白酶裂解的位点。在电子显微镜下，经负染色的游离α2M可与游离α1M区分开来。放射性标记的α2M从血浆中清除缓慢，但该蛋白与标记的枯草杆菌蛋白酶的复合物以一级动力学迅速清除，半衰期约为6分钟。这些复合物主要被肝脏摄取，这与先前对α1M - 枯草杆菌蛋白酶复合物的描述一致。两种巨球蛋白的复合物相互竞争摄取，表明通过共同受体进行内吞作用。
