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Proton transfer in and polarizability of hydrogen bonds coupled with conformational changes in proteins. II. IR investigation of polyhistidine with various carboxylic acids
Author(s) -
Lindemann Rainald,
Zundel George
Publication year - 1978
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.1978.360170514
Subject(s) - chemistry , hydrogen bond , histidine , protonation , aspartic acid , polarizability , proton , amide , carboxylic acid , peptide bond , low barrier hydrogen bond , carboxylate , stereochemistry , crystallography , molecule , amino acid , ion , organic chemistry , enzyme , biochemistry , physics , quantum mechanics
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 p K a of 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 Δp K a values 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, and in proteases, whereby this type of bond is preferentially found in the active centers of these enzymes. It is pointed out that hydrogen bonds with such interaction properties should be of great significance for structure and especially functions of proteins in which they are present.