Parham P, Brodsky F M, Drickamer K
Department of Cell Biology, Stanford University, CA 94305.
Biochem J. 1989 Feb 1;257(3):775-81. doi: 10.1042/bj2570775.
Three forms of clathrin light chain contain two cysteine residues. These are the predominant brain-specific forms of LCa and LCb and the non-brain form of LCb. After purification in the absence of thiols they contain intramolecular disulphide bonds. The reduced and the oxidized forms show differences in electrophoretic mobility, explaining the variable and heterogeneous patterns observed on electrophoresis. Accessibility of the thiol groups in the free light chains is greater than when they are associated with the heavy chain. In contrast the cysteine residues of the clathrin heavy chain are completely inaccessible in the absence of denaturants and are not found in disulphide bonds. The antigenic properties of the oxidized and the reduced forms of the clathrin light chains are similar, as is their capacity to bind to the clathrin heavy chain. After isolation in the presence of 10 mM-iodoacetamide, the light-chain cysteine residues are fully alkylated. The results are consistent with the reduced form being the native state and the light-chain disulphide bonds an artifact of isolation.
三种形式的网格蛋白轻链含有两个半胱氨酸残基。这些是主要的脑特异性轻链a和轻链b形式以及非脑型轻链b。在无硫醇的情况下纯化后，它们含有分子内二硫键。还原形式和氧化形式在电泳迁移率上存在差异，这解释了电泳时观察到的可变且不均一的条带模式。游离轻链中硫醇基团的可及性大于其与重链结合时的可及性。相反，在没有变性剂的情况下，网格蛋白重链的半胱氨酸残基完全不可及，并且不存在于二硫键中。网格蛋白轻链氧化形式和还原形式的抗原特性相似，它们与网格蛋白重链结合的能力也相似。在10 mM碘乙酰胺存在下分离后，轻链半胱氨酸残基被完全烷基化。结果表明还原形式是天然状态，而轻链二硫键是分离过程中的假象。
