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

Desulfovibrio africanus ferredoxin I was studied by magnetic circular dichroism and H-1-NMR spectroscopies. These showed the presence of his tidine and tryptophan, in contrast to the previously reported amino-ac id sequence (Bruschi and Hatchikian (1982) Biochimie 64, 503-507). Thi s was redetermined and the revised sequence shown to contain both hist idine and tryptophan, as well as four other corrections (Sery et al. ( 1994) Biochemistry, submitted). Electrospray mass spectrometry confirm ed the mass of the ferredoxin was that given by the revised amino-acid sequence. The secondary structure of the ferredoxin I was investigate d with two-dimensional H-1-NMR experiments and both alpha-helix and be ta-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 conclu ded that there is only a negligible dipolar contribution to resonance chemical shifts from this source. The significance of this for the det ermination of the three-dimensional structure of the ferredoxin by NMR is discussed.