Dobson N, Melcher U
Biochem J. 1979 Nov 1;183(2):395-403. doi: 10.1042/bj1830395.
In order to explore structural differences between membrane and secreted immunoglobulins the buoyant densities of mouse immunoglobulin (Ig) heavy (H) chains were compared by isopycnic centrifugation in CsCl containing guanidine hydrochloride. The buoyant densities, under denaturing conditions, of mouse myeloma protein MOPC 21 IgG, MOPC 315 IgA and MOPC 104E IgM H chains were consistent with their carbohydrate contents. Mouse membrane IgM and MOPC 104E-secreted IgM H chains were of equal density. The buoyant densities of MOPC 104E-secreted IgM and spleen-cell-secreted IgM H chains were indistinguishable. The IgD-like membrane H chain was denser than membrane IgM H chain, and its carbohydrate content was calculated to be 15.5%. The resolution of the technique was sufficient to conclude that the apparent 1500 mol.wt. difference, as determined by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, between membrane and secreted IgM H chains was due to peptide rather than to carbohydrate. The results also imply that intact membrane IgM and IgD bind detergent and are thus integral membrane proteins.
为了探究膜结合型免疫球蛋白与分泌型免疫球蛋白之间的结构差异，通过在含有盐酸胍的氯化铯中进行等密度离心，比较了小鼠免疫球蛋白（Ig）重链（H链）的浮力密度。在变性条件下，小鼠骨髓瘤蛋白MOPC 21 IgG、MOPC 315 IgA和MOPC 104E IgM H链的浮力密度与它们的碳水化合物含量一致。小鼠膜IgM和MOPC 104E分泌的IgM H链密度相等。MOPC 104E分泌的IgM和脾细胞分泌的IgM H链的浮力密度无法区分。类IgD膜H链比膜IgM H链密度大，其碳水化合物含量经计算为15.5%。该技术的分辨率足以得出结论，即通过十二烷基硫酸钠/聚丙烯酰胺凝胶电泳测定的膜结合型与分泌型IgM H链之间明显的1500道尔顿分子量差异是由肽而非碳水化合物造成的。结果还表明，完整的膜IgM和IgD能结合去污剂，因此是整合膜蛋白。
