Ferredoxin and Rubredoxin from Butyribacterium methylotrophicum: Complete Primary Structures and Construction of Phylogenetic Trees1

Complete ami no acid sequences of ferredoxin and rubredoxin from Butyribacterium methylotrophicum, a methylotrophic hetero-acetogen, were determined by combination of protease digestion, Edman degradation, carboxypeptidase digestion, and/or partial acid hydrolysis. The ferredoxin was composed of 55 amino acids with a molecular weight of 5,732 excluding iron and sulfur atoms and showed a typical 2[4Fe-4S]-type ferredoxin sequence with an internal repeat at the 14-23 and 42-51 positions. The rubredoxin was composed of 53 amino acids with a molecular weight of 5,672 excluding iron atom and showed a sequence similar to those of other anaerobic rubredoxins. The sequences were compared to those of corresponding proteins from six different bacteria to construct phylogenetic trees, which showed essentially the same topology. The relationships between the ferredoxin sequences from this bacterium and those of Clostridium thermoaceticum and Afethanosarcina barkeri, both of which possess a carbonyl-dependent acetyl-CoA metabolic system, are also discussed. Ferredoxin is a non-heme iron-sulfur electron carrier protein widely distributed among prokaryotes (1). Th