MCD AND H-1-NMR SPECTROSCOPIC STUDIES OF DESULFOVIBRIO-AFRICANUS FERREDOXIN-I - REVISED AMINO-ACID-SEQUENCE AND IDENTIFICATION OF SECONDARY STRUCTURE

Desulfovibrio africanus ferredoxin I was studied by magnetic circular dichroism and H-1-NMR spectroscopies. These showed the presence of histidine and tryptophan, in contrast to the previously reported amino-acid sequence (Bruschi and Hatchikian (1982) Biochimie 64, 503-507). This was redetermined and the revised sequence shown to contain both histidine and tryptophan, as well as four other corrections (Sery et al. (1994) Biochemistry, submitted). Electrospray mass spectrometry confirmed the mass of the ferredoxin was that given by the revised amino-acid sequence. The secondary structure of the ferredoxin I was investigated with two-dimensional H-1-NMR experiments and both alpha-helix and beta-sheet structure detected. The influence of the paramagnetism of the Fe-4 S-4 cluster on the NMR properties of the ferrredoxin protons was investigated, by temperature-dependent experiments, and it was concluded that there is only a negligible dipolar contribution to resonance chemical shifts from this source. The significance of this for the determination of the three-dimensional structure of the ferredoxin by NMR is discussed.