NMR-STUDIES OF THE ALPHA-CHYMOTRYPSIN-(R)-1-ACETAMIDO-2-(4-FLUOROPHENYL)ETHANE-1-BORONIC ACID COMPLEX AT PH-7

The interaction of (R)-1-acetamido-2-(4-fluorophenyl)ethane-1-boronic acid with alpha-chymotrypsin at pH 7 was studied by a variety of fluorine and proton NMR experiments and the results compared to observations made at pH 4. It was demonstrated that this compound forms a complex with a 1:1 stoichiometry at pH 7; proton NMR indicates that the boronic acid likely is coordinated to the serine-195 residue at the active site. Analysis of fluorine T-1 relaxation behavior and F-19(H-1) NOE data shows that the rate constant for dissociation of the complex is 4.7 s(-1), somewhat faster than is observed at pH 4. The data analysis and the results of two-dimensional F-19(H-1) NOE experiments show that interactions between the fluoroaromatic ring of the inhibitor and the enzyme are weaker at the higher pH value, although the motion of the fluoroaromatic ring within the complex appears to be just as restricted as is the case at pH 4.