Sensitive Cu2+–Cu2+DistanceMeasurements in a Protein–DNA Complex by Double-Quantum CoherenceESR.

Double quantum coherence (DQC) ESRspectroscopy is applied to measurethe Cu2+–Cu2+distance in the EcoRI-DNAcomplex. A simple method is proposed to reduce the contribution ofnuclear hyperfine and quadrupole interactions to such data. The effectsof such interactions between the electron spin of Cu2+andneighboring nuclei on the DQC data make it difficult to measure thenanometer range interspin distance. The DQC data is in good agreementwith results obtained by double electron electron resonance (DEER)spectroscopy. At the same time, the signal-to-noise ratio per shotin DQC is high. Taken together, these results provide impetus forfurther development of paramagnetic metal ion-based DQC techniques. [ABSTRACT FROM AUTHOR]