The detection of proline isomerase activity in FK506-binding protein by two-dimensional 1H NMR exchange spectroscopy

1H NMR assignments of the trans and cis isomers of succinyl-Ala-Ala-Pro-Phe-p-nitroanilide were accomplished by two-dimensional NMR techniques. Conformational exchange between the cis and trans isomers was not detected in the two-dimensional exchange spectra (NOESY) until catalytic amounts of FK506-binding protein (FKbp) were added. The addition of FK506 to the enzyme-substrate solution inhibited the enzyme and removed the substrate exchange peaks.