title: Motion at the active site of [(4-fluorophenyl)sulfonyl]chymotrypsin.
abstract: Fluorine and deuterium NMR relaxation studies have been used to examine the motion of the 4-fluorophenyl ring attached to the active site of [(4-fluorophenyl)sulfonyl]-alpha-chymotrypsin at pH 4. Analysis of the results indicates that rotation about the 2-fold axis of this ring is reasonably rapid, though not as fast as in tosylchymotrypsin. Two-dimensional (2D) nuclear Overhauser effects (NOEs) were used to suggest the shifts of those protons of the enzyme close enough to the fluorine nucleus to lead to relaxation; important proton-fluorine dipolar relaxation contributions arise from protons with shifts of 7.4 +/- 0.3 ppm and between 4.0 and 5.4 ppm. Specific deuteration permits the assignment of the first of these to the protons ortho to the fluorine while serine-189, cysteines-191 and -220, and methionine-192 are suggested as possible bearers of the other protons. The fluorine chemical shift effect observed for the native conformation of this protein is 9 ppm downfield of the shift observed with the denatured protein; this large shift may be the result of van der Waals interactions between the fluorine and one or more of the protons whose signals appear in the 2D NOE experiments.
mesh_terms: D001665:Binding Sites; D002918:Chymotrypsin / Q000378:metabolism*; D003903:Deuterium; D005461:Fluorine; D005464:Fluorobenzenes / Q000138:chemical synthesis / Q000494:pharmacology*; D007202:Indicators and Reagents; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D013450:Sulfones / Q000138:chemical synthesis / Q000494:pharmacology*
chemical_list: D005464:Fluorobenzenes; D007202:Indicators and Reagents; D013450:Sulfones; D005461:Fluorine; C050355:4-fluorobenzenesulfonyl fluoride; D003903:Deuterium; D002918:Chymotrypsin