Bailyes E M, Soos M, Jackson P, Newby A C, Siddle K, Luzio J P
Biochem J. 1984 Jul 15;221(2):369-77. doi: 10.1042/bj2210369.
Immunoaffinity-purified rat liver 5'-nucleotidase contained two subunits of Mr 70 000 (alpha) and 38 000 (beta). Charge-shift electrophoresis and chemical cross-linking revealed that approx. 80% of the solubilized enzyme activity occurred as an alpha alpha-dimer of Mr 140 000. The remaining 20% was an alpha beta-dimer of Mr 108 000. The beta-subunit did not possess enzymic activity. Peptide mapping and immunoblotting with antibodies against the alpha- and beta-subunits showed that the beta-subunit was homologous with a part of the alpha-subunit. Three monoclonal antibodies against rat liver 5'-nucleotidase were characterized as binding to the extracellular domain of the enzyme. All three monoclonal antibodies and concanavalin A bound to the alpha-subunit, but no binding could be detected to the beta-subunit. It was therefore concluded that the beta-subunit was a fragment of an alpha-subunit that had lost an extracellular domain. Both forms of the enzyme occurred in freshly solubilized membrane preparations as well.
免疫亲和纯化的大鼠肝脏5'-核苷酸酶含有分子量为70000（α）和38000（β）的两个亚基。电荷位移电泳和化学交联显示，约80%的可溶酶活性以分子量为140000的αα二聚体形式存在。其余20%是分子量为108000的αβ二聚体。β亚基不具有酶活性。肽图谱分析以及用抗α和β亚基的抗体进行免疫印迹表明，β亚基与α亚基的一部分同源。三种抗大鼠肝脏5'-核苷酸酶的单克隆抗体被鉴定为与该酶的细胞外结构域结合。所有三种单克隆抗体和伴刀豆球蛋白A都与α亚基结合，但未检测到与β亚基的结合。因此得出结论，β亚基是α亚基失去细胞外结构域后的片段。这两种形式的酶也存在于刚溶解的膜制剂中。
