14,15N, 13C, 57Fe, and 1,2H Q-band ENDOR study of Fe-S proteins with clusters that have endogenous sulfur ligands.

The benefits of performing ENDOR experiments at higher microwave frequency are demonstrated in a Q-band (35 GHz) ENDOR investigation of a number of proteins with [nFe-mS] clusters, n=2, 3, 4. Each protein displays several resonances in the frequency range of 0-20 MHz. In all instances, features are seen near v≃13 and 8 MHz that can be assigned, respectively, to «distant ENDOR» from 13 C in natural-abundance (1.1%) and from 14 N (the Δm I =±2 transitions); the nuclei involved in this phenomenon are remote from and have negligible hyperfine couplings to the cluster