I. Bertini et al., H-2 NMR INVESTIGATION OF [FE3S4](0) CLUSTER IN 7FE8S FERREDOXIN FROM BACILLUS-SCHLEGELII, Inorganic chemistry, 37(5), 1998, pp. 969-972
A H-2 NMR study has been performed on a 7Fe8S ferredoxin from Bacillus
schlegelii which has been overexpressed in Escherichia coli. The prot
ein cysteines have been deuterated at the beta position by incorporati
ng labeled cysteines into the growth media. The protein contains an Fe
3S4 and an Fe4S4 cluster. The former has been investigated in the [Fe3
S4](0) and in the [Fe3S4](+) states. Whereas the [Fe3S4](+)-containing
species provides sharp H-1 and H-2 NMR spectra for the signals of the
cysteine ligands, no corresponding H-1 or H-2 signals have been detec
ted from the [Fe3S4](0)-containing species. Theoretical considerations
predict observability of these signals unless a chemical equilibrium
is operative. It is proposed therefore that the Fe3+ ion and the two F
e2.5+ ions constituting the cluster exchange their valency with a rate
in the order of 10(6) s(-1), which would cause coalescence of the sig
nals.