Proton transfer in and polarizability of hydrogen bonds coupled with conformational changes in proteins. II. IR investigation of polyhistidine with various carboxylic acids

作者：Rainald Lindemann, George Lorenzo Ingram Zundel · 发表于：Biopolymers · 年份：1978 · DOI：10.1002/bip.1978.360170514 · 被引用次数：30 · 研究领域：Hemoglobin structure and function、Protein Structure and Dynamics、Mass Spectrometry Techniques and Applications

Abstract Polyhistidine‐carboxylic acid systems are studied by ir spectroscopy. It is shown that OH ⃛N ⇌ O−…H+N bonds formed between carboxylic groups and histidine residues are easily polarizable proton‐transfer hydrogen bonds when the pKaof the protonated histidine residues is about 2.8 units larger than that of the carboxylic groups. From these results it bis concluded that OH ⃛N ⇌ O−⃛H+N bonds between glutamic or aspartic acid histidine residues in proteins may be easily polarizable proton‐transfer bonds. Furthermore, it is demonstrated that water molecules shift the proton‐transfer equilibria in these hydrogen bonds in favor of the polar structure, i.e., due to water or polar environments OH ⃛N ⇌ O−⃛H+N bonds with smaller ΔpKavalues become easily polarizable proton‐transfer hydrogen bonds. A consideration of the amide bands of polyhistidine shows that it can be present in five different conformations. It is shown that these conformational changes are strongly related to the degree of proton transfer. Hence, the degree of proton transfer, the degree of hydration, and conformation are not independent of each other, but are strongly coupled. Further proof for the interdependence of proton transfer and conformational changes are hysteresis effects, which are observed with studies of polyhistidine dependent on carboxylic acid, adsorption and desorption. OH ⃛N ⇌ O−⃛H+N bonds between aspartic and glutamic acid and histidine residues are present in hemoglobin, in ribonucleases, a...