Holloway P W, Mantsch H H
Division of Chemistry, National Research Council of Canada, Ottawa, Ontario.
Biochemistry. 1988 Oct 18;27(21):7991-3. doi: 10.1021/bi00421a003.
The infrared spectrum of a solution of a protein contains bands due to both the peptide backbone and the amino acid side chains. Generally, the bands due to the peptide backbone, between 1700 and 1600 cm-1, are analyzed to determine the secondary structure of the protein; the bands due to the amino acid side chains, between 1600 and 1500 cm-1, are largely ignored. When cytochrome b5 is mixed with cytochrome c, under conditions that favor ionic complex formation, changes are seen in protein secondary structure and also in a band at 1562 cm-1. The band at 1562 cm-1 is due to the side-chain carboxyl of Glu residues, rather than those of Asp residues that show a band at 1585 cm-1, and the changes in the band at 1562 cm-1 indicate that when the two proteins interact, three ionized carboxyl groups of Glu become involved in salt bridge formation. This result is identical with that obtained by previous theoretical studies and suggests that infrared spectroscopy may be a rapid and quantitative method for the study of ionic interactions between proteins.
蛋白质溶液的红外光谱包含肽主链和氨基酸侧链产生的谱带。一般来说，位于1700至1600 cm-1之间的肽主链产生的谱带用于分析确定蛋白质的二级结构；而位于1600至1500 cm-1之间的氨基酸侧链产生的谱带在很大程度上被忽略。当细胞色素b5与细胞色素c在有利于离子复合物形成的条件下混合时，蛋白质二级结构以及1562 cm-1处的谱带都会出现变化。1562 cm-1处的谱带是由谷氨酸残基的侧链羧基产生的，而非天冬氨酸残基（其在1585 cm-1处有谱带），1562 cm-1处谱带的变化表明，当这两种蛋白质相互作用时，三个离子化的谷氨酸羧基参与了盐桥的形成。这一结果与先前理论研究所得结果一致，表明红外光谱法可能是一种快速且定量研究蛋白质间离子相互作用的方法。
