Lapuk V A, Khatiashvili N M, Chukhrova A I, Kaverzneva E D
Biokhimiia. 1985 Feb;50(2):237-42.
The modification of tryptophan residues in monoclonal immunoglobulin M (IgM) by 2-hydroxy-5-nitrobenzyl bromide (RK) was studied at pH 2.0-2.85 and 7.0 and a RK to tryptophan molar ratio (K) from 1 to 40. At pH 2.85, the number of RK residues bound to IgM (N) in account to one HL-fragments does not exceed 10 (the HL-fragment of IgM contains 14 tryptophan residues); the plot of N vs K reaches a plateau at K greater than 20. When the pH is lowered to approximately 2, N rises to approximately 15, but the plateau is not reached. At pH 7.0, the modified IgM with N greater than 1 gives a sediment, while the product with N approximately equal to 1 remains in solution. Evidently, the latter contains the most accessible tryptophan residue (calculated per one HL-fragment). This residue was found to be one of the three residues localized in the C mu 2-domain and the adjoining N-terminal part. The possibility of multiple modification of tryptophan residues during the RK interaction with IgM in acid medium at high values of K is discussed.
在pH值为2.0 - 2.85和7.0以及2-羟基-5-硝基苄基溴（RK）与色氨酸的摩尔比（K）为1至40的条件下，研究了2-羟基-5-硝基苄基溴（RK）对单克隆免疫球蛋白M（IgM）中色氨酸残基的修饰作用。在pH 2.85时，与一个HL片段结合的RK残基数量（N）不超过10（IgM的HL片段含有14个色氨酸残基）；N对K的曲线在K大于20时达到平稳期。当pH值降至约2时，N上升至约15，但未达到平稳期。在pH 7.0时，N大于1的修饰IgM会产生沉淀，而N约等于1的产物则保留在溶液中。显然，后者含有最易接近的色氨酸残基（按一个HL片段计算）。该残基是位于Cμ2结构域和相邻N端部分的三个残基之一。讨论了在高K值的酸性介质中，RK与IgM相互作用时色氨酸残基发生多重修饰的可能性。
