Nuclear magnetic resonance studies of the interaction of inhibitors with chymotrypsin. N-Trifluoroacetyl derivatives of phenylalanine

Abstract

The binding of N-trifluoroacetyl derivatives of phenylalanine to the enzyme chymotrypsin has been studied by ¹⁹F nuclear magnetic resonance spectroscopy. Separate resonances are observed for the D- and L- enantiomers in the presence of chymotrypsin and their difference in chemical shift is dependent on the molar ratio of inhibitor to enzyme. The results are interpreted in terms of the known structure of the active site and possible modes of reorientation of the aromatic ring in its binding site. Approximate and accurate methods of quantifying the data are discussed and values for the dissociation constant (K_I) of the EI complex, and the change in chemical shift on binding, are reported for the D-isomers.