Structural homologies between the amino acid sequence of Clostridium pasteurianum MoFe protein and the DNA sequences of nifD and K genes of phylogenetically diverse bacteria

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Abstract
The complete amino acid sequence of the larger (α‐) subunit and about 70% of the total sequence of the smaller (β‐) subunit of the MoFe protein from Clostridium pasteurianum was determined by analyses of peptides derived from BrCN cleavage and by digestions with trypsin, staphylococcal protease and lysylendo‐peptidase of the separated subunits. The α‐subunit has 529 amino acid residues, giving an M r value of 58 774. This is the first complete sequence for the α‐subunit of an isolated MoFe protein. In comparing the sequences of both subunits to those from other sources, 5 out of 9 cysteines in the α‐subunit and 3 out of 6 in the β‐subunit are invariant, thus suggesting a function as ligands to FeS and MoFeS clusters in the MoFe protein. All of these cysteines are located in the amino terminal halves of both subunits.