Imamura T, Konishi K
Department of Biophysical Chemistry, Dokkyo University School of Medicine, Tochigi, Japan.
J Protein Chem. 1992 Jun;11(3):289-303. doi: 10.1007/BF01024868.
The changes of microenvironment of tryptophan residues in beta-lactoglobulin A and its cyanogen bromide (CNBr) fragments with the binding of sodium dodecyl sulfate (SDS) were studied with measurements of the rates of N-bromosuccinimide (NBS) modification reactions by stopped-flow photometry. Two tryptophan residues of carboxyamidomethylated (RCM) beta-lactoglobulin A in the states of their complexes with SDS were clearly distinguishable by their differences in NBS modification rates. We confirmed by experiments with CNBr fragments containing trytophan residue. The modification rates of Trp 19 in RCM beta-lactoglobulin A-SDS complexes were about 10-fold smaller than those expected for tryptophan residues exposed entirely to the aqueous solvent. The Trp 61 was hardly changed. The change of rate constants for Trp 19 was virtually consistent with those observed when N-acetyl-L-trytophan ethylester was dissolved in SDS micelles. For various species of polypeptide-SDS complexes, all tryptophan residues were reactive to NBS and also, for some of them, the differences in NBS modification rates were observed between tryptophan residues on a common polypeptide chain. These results suggest micellar and heterogeneous bindings of SDS to polypeptides.
通过停流光度法测量N-溴代琥珀酰亚胺（NBS）修饰反应的速率，研究了β-乳球蛋白A及其溴化氰（CNBr）片段中色氨酸残基微环境随十二烷基硫酸钠（SDS）结合的变化。羧基酰胺甲基化（RCM）β-乳球蛋白A与SDS形成复合物时，其中的两个色氨酸残基在NBS修饰速率上存在差异，从而得以清晰区分。我们通过含色氨酸残基的CNBr片段实验进行了证实。RCMβ-乳球蛋白A-SDS复合物中Trp 19的修饰速率比完全暴露于水性溶剂中的色氨酸残基预期的修饰速率小约10倍。Trp 61几乎没有变化。Trp 19的速率常数变化实际上与N-乙酰-L-色氨酸乙酯溶解于SDS胶束中时观察到的情况一致。对于各种多肽-SDS复合物，所有色氨酸残基都对NBS有反应，而且对于其中一些复合物，在同一条多肽链上的色氨酸残基之间也观察到了NBS修饰速率的差异。这些结果表明SDS与多肽存在胶束结合和异质结合。
