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1 H‐Nuclear magnetic resonance study on imidazole–imidazole interaction in L ‐histidyl‐ L ‐histidine and D ‐histidyl‐ L ‐histidine: Analysis including microscopic dissociation series
Author(s) -
Tanokura Masaru
Publication year - 1983
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.360221210
Subject(s) - histidine , imidazole , chemistry , dissociation (chemistry) , titration , crystallography , titration curve , stereochemistry , nuclear magnetic resonance , biochemistry , amino acid , physics
The 1 H‐nmr titration curves of chemical shifts versus pH were observed for the protons of D,L ‐histidyl‐ D,L ‐histidine as representative of cases with two or more ionizable groups with similar p K a values. The titration curves of L ‐histidyl‐ L ‐histidine and D ‐histidyl‐ L ‐histidine were individually analyzed according to two mathematical models: one of a macroscopic dissociation series and one of a microscopic dissociation series. Most‐probable values and standard deviations were obtained for p K a values and intrinsic chemical shifts. An analysis including the microscopic dissociation series yielded an electrostatic interaction between twoimidazole rings of about 0.3 pH units for L ‐histidyl‐ L ‐histidine and about 0.7 pH units for D ‐histidyl‐ L ‐histidine. The difference of the magnitude of imidazole‐imidazole interactions between L ‐histidyl‐ L ‐histidyne and D ‐histidyl‐ L ‐histidine was interpreted in terms of the spatial arrangement of two imidazole rings in each molecule based on the solution conformation estimated from Gd(III)‐induced relaxation enhancements.