CHEMICAL-EXCHANGE SPECTROSCOPY BASED ON C-13 NMR - APPLICATIONS TO ENZYMOLOGY AND PROTEIN FOLDING

We explore how 13C-based two-dimensional chemical exchange spectroscopy (EXSY) can be used to investigate exchange processes that are slow on the NMR time scale. Results are shown for the mutarotase-catalyzed α →← β isomerization of [1-13C]glucose using experiments that detect carbon spins: homonuclear 13C exchange spectroscopy [13C {13C} EXSY] and heteronuclear exchange spectroscopy [13C {1H} EXSY]; and inverse experiments that select for proton spins attached to 13C: 1H- 13C single-bond correlation exchange spectroscopy [1H {13C} SBC-EXSY] and 13C-filtered 1H exchange spectroscopy [1H{1H}-13Cf{hook}-EXSY]. The main advantage of 13C-based exchange experiments is the simplification of complex spectra afforded by incorporation of selective labels. The inherent power of this approach is illustrated with a 1H {13C} SBC-EXSY spectrum showing the native →← denatured interconversion of [13Cδ1] Trp-staphylococcal nuclease. Certain 13C-based EXSY experiments are useful for discriminating exchange connectivities from dipole-dipole connectivities. © 1990.