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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