Thermodynamics of cyclophilin catalyzed peptidyl‐prolyl isomerization by nmr spectroscopy

One‐dimensional nmr exchange spectroscopy was carried out to determine thermodynamic parameters of cyclophilin‐induced cis ‐ trans isomerization of succinyl‐Ala‐Phe‐Pro‐Phe‐ p ‐nitroanilide. Rate measurements were possible at physiological temperatures. The k c / K m of rat cyclophilin was found to he 12.8 (±0.5) s −1 μ M −1 at 37°C, intermediate to previously reported values that used a coupled enzyme assay extrapolated to this temperature. Activation energies (Δ G ≠ ) for the uncatalyzed and catalyzed reaction at 37°C were found to be 19.7 and 17.1 kcal/mol, respectively, and were primarily due to an enthalpic barrier. © 1994 John Wiley & Sons, Inc.