Electron self-exchange of cytochrome c measuredvia13Cdetected protonless NMR

Abstract

The use of protonless13C′–13C′ EXSY (COCO-EXSY) is proposed here to measure electron self-exchange rates. The experiment is compared to the commonly employed1H and15N EXSY experiments using as a reference system human cytochrome c. In COCO-EXSY, the exchange peaks are stronger than in the other experiments with respect to the self peaks and their intensity is less dependent on the choice of the EXSY mixing time. The use of13C directed detection may be essential for all those cases where T2relaxation is detrimental, as in the case of proteins containing highly paramagnetic metal centers, or rotating slowly in solution, or where the amide signals are difficult to detect due to chemical or conformational exchange. The proposed experiment has a general applicability and can be used to monitor exchange phenomena different from electron self-exchange.