Studies of the kinetics of the interaction between N‐trifluoroacetlyl‐ D ‐tryptophan and α‐chymotrypsin by pulsed nuclear magnetic resonance

The Carr‐Purcell experiment first used by Allerhand and Gutowsky for the determination of chemical exchange rates has been applied to the study of an enzyme inhibitor complex. Chemical shift and relaxation time data obtained by analysis of pulsed fluorine NMR data collected at 51 MHz are shown to be consistent with high resolution results assembled at 94° 1 MHz. The rate constants for dissociation of the N‐trifluoroacetyl‐D‐tryptophan‐α‐chymotrypsin complex were determined to be 1 × 104 s−1 at 26°C and 2 × 103 s−1 at 6·5°C. The resonance position of the fluorine nuclei of the inhibitor is shifted downfield ∼1 ppm upon complexation to the enzyme, and the trifluoromethyl group suffers some restriction of molecular motion in the bound state as indicated by T1 and T2 data.