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Structurally symmetrical, easily polarizable hydrogen bonds between side chains in proteins and proton‐conducting mechanisms. III
Author(s) -
Kristof Wolfgang,
Zundel Georg
Publication year - 1980
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.1980.360191006
Subject(s) - chemistry , hydrogen bond , protonation , polarizability , crystallography , deprotonation , proton , side chain , low barrier hydrogen bond , computational chemistry , stereochemistry , molecule , ion , organic chemistry , physics , quantum mechanics , polymer
( L ‐Cys) n , ( L ‐Lys) n , and ( L ‐Glu) n were studied by ir spectroscopy in terms of their degree of deprotonation or protonation. It is shown that structurally symmetrical, easily polarizable SH ⃛S − ⇌ − S ⃛HS, N + H ⃛N ⇌ N ⃛H + N, and OH ⃛O − ⇌ − O ⃛HO hydrogen bonds are formed between the side chains. The different wave number distributions of the ir continua caused by these hydrogen bonds show that the barrier in the double‐minimum proton potential decreases in the series of these hydrogen bonds. The stability of these hydrogen bonds against hydration increases in this series. The OH ⃛O − ⇌ − O ⃛HO bonds are not broken by small amounts of water. With ( L ‐Cys) n the formation of easily polarizable hydrogen bonds and a β‐structure–coil transition are strongly interdependent. As a result of this coupling effect, the β‐structure–coil transition becomes cooperative. With ( L ‐Glu) n , the formation of the polarizable hydrogen bonds and the observed conformational change are independent processes. The ( L ‐Glu) n conformation changes from α‐helix to coil only if more than 80% of the residues are deprotonated. Finally, on the basis of the various types of easily polarizable hydrogen bonds, charge shifts in active centers of enzymes and the proton‐conducting mechanism through hydrophobic regions of biological membranes are discussed.