The occupancy of two distinct conformations by active‐site histidine‐119 in crystals of ribonuclease is modulated by pH
- 25 July 1994
- journal article
- research article
- Published by Wiley in FEBS Letters
- Vol. 349 (1), 155-160
- https://doi.org/10.1016/0014-5793(94)00664-4
Abstract
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 pK 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.Keywords
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