Karlsson F A, Peterson P A, Berggard I
Proc Natl Acad Sci U S A. 1969 Dec;64(4):1257-63. doi: 10.1073/pnas.64.4.1257.
Light polypeptide chains from both normal human gammaG immunoglobulin and Bence-Jones proteins can be cleaved into halves by limited proteolysis with trypsin, pepsin, or papain. The fragments were obtained in yields of up to 22 per cent, had molecular weights of 10,000 to 11,000, and were shown by amino acid analysis and antigenic analysis to correspond to variable or constant regions of light chains. Starch gel electrophoresis in urea suggested that each half consisted of a single polypeptide chain. A fragment from the urine of a myeloma patient corresponded almost exactly to the constant half of a gamma-chain and had a compact shape (Stokes radius of 16 A; frictional ratio of 1.1). Similar Stokes radii were estimated both on fragments from normal urine and fragments produced by proteolysis of normal light chains. The results are consistent with the view that most urinary fragments have a catabolic origin and suggest that there is a small stretch of polypeptide chain between the compact V and C regions of light chains which is particularly susceptible to proteolysis. This lends support to the hypothesis that immunoglobulin chains consist of globular domains connected by more extended stretches of polypeptide chain.
正常人γG免疫球蛋白和本斯·琼斯蛋白的轻多肽链，可用胰蛋白酶、胃蛋白酶或木瓜蛋白酶进行有限的蛋白水解，切成两半。这些片段的产率高达22%，分子量为10,000至11,000，通过氨基酸分析和抗原分析表明，它们对应于轻链的可变区或恒定区。在尿素中进行淀粉凝胶电泳表明，每一半都由一条单一的多肽链组成。一位骨髓瘤患者尿液中的一个片段几乎与γ链的恒定半段完全对应，且形状紧密（斯托克斯半径为16埃；摩擦比为1.1）。对正常尿液中的片段以及正常轻链经蛋白水解产生的片段，估计其斯托克斯半径相似。这些结果与大多数尿液片段具有分解代谢起源的观点一致，并表明在轻链紧密的V区和C区之间存在一小段多肽链，特别容易受到蛋白水解作用。这支持了免疫球蛋白链由通过更长的多肽链延伸段连接的球状结构域组成的假说。
