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The occupancy of two distinct conformations by active‐site histidine‐119 in crystals of ribonuclease is modulated by pH
Author(s) -
J. de Mel V.Srini,
Doscher Marilynn S.,
Martin Philip D.,
Edwards Brian F.P.
Publication year - 1994
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(94)00664-4
Subject(s) - histidine , chemistry , active site , residue (chemistry) , crystallography , rnase p , ribonuclease , stereochemistry , side chain , ribonuclease t1 , substrate (aquarium) , enzyme , biochemistry , organic chemistry , biology , rna , gene , polymer , ecology
Structures of a semisynthetic RNase have been obtained to a resolution of 2.0 Å at pH values of 5.2, 6.5, 7.5, and 8.8, respectively. The principle structural transformation occurring over this pH range is the conversion of the side chain of active site residue His‐119 from one conformation ( X 1 = −43° to −57°) at low pH to another ( X 1 = + 159° to + 168°) at higher pH values. On the basis of this observation, a model is proposed that reconciles the disparate p K values for His‐119 in the enzyme‐substrate complex that have been deduced from kinetic studies and from proton NMR measurements in the presence of pseudosubstrates.