This paper presents the results of 2H Mims and 1H Davies pulsed ENDOR of the [3Fe-4S]+ cluster of Desulfovibrio gigas hydrogenase. It also describes the first 2H Mims pulsed TRIPLE-resonance experiments, on the exchangeable deuterons. The 1H ENDOR data show that the intrinsic isotropic hyperfine couplings for the β-CH2protons of the three cysteines bound to iron fall in the range 1.3 ≲ a ≲ 1.9 MHz. These values, which often had been estimated at a = 1 MHz, will allow better interpretation of solution NMR data for paramagnetic [nFe-wS] clusters. The spectra show well-resolved signals from three strong NH…S H-bonds to the cluster. Mims 2H-2H TRIPLE-resonance has been used to assign the exchangeable deuterons and to obtain relative signs of the 1, 2H hyperfine couplings. Analysis of the hyperfine interactions in terms of spin-coupling among the three Fe(III) ions of the cluster, along with examination of the X-ray structures of several [3Fe-4S]+ clusters, gives an intrinsic hyperfine coupling of a(1H) ~ 3-4 MHz for each of the three strong H-bonds and actually allows us to propose the distribution of H-bonds among the seven sulfur atoms within the [Fe3S4(Cys)3]2- center.
ASJC Scopus subject areas
- Colloid and Surface Chemistry