CYTOCHROMES C-552 FROM 2 STRAINS OF THE HYDROGENOTROPHIC BACTERIUM ALCALIGENES-EUTROPHUS ARE SEQUENCE HOMOLOGS OF THE CYTOCHROMES C(8) FROMTHE DENITRIFYING PSEUDOMONADS

Soluble cytochromes c-552 were purified from two strains of the hydrog enothrophic species Alcaligenes eutrophus and their amino acid sequenc es determined. The two cytochromes were found to have 5 differences ou t of a total of 89 residues. The proteins are clearly related to the c ytochromes c(8) (formerly called Pseudomonas cytochromes c-551), but r equire a single residue insertion after the methionine sixth heme liga nd relative to the Pseudomonas aeruginosa protein. The consensus resid ues Trp56 and Trp77. characteristic for the c(8) family, are also pres ent in the Alcaligenes proteins. Overall, the Alcaligenes cytochromes are only 43% identical to the Pseudomonas proteins which average 68% i dentity to one another. They are also only 45% identical to cytochrome c(8) from Hydrogenobacter thermophilus, another hydrogenothrophic spe cies, which indicates that the hydrogen utilizing bacteria are not mor e closely related to one another than they are to other species. The f inding of cytochrome c(8) in Alcaligenes eutrophus completes the recen t characterization of a cytochrome cd(1)-nitrite reductase from this b acterial species and suggests the existence of the same denitrificatio n pathway as in Pseudomonas where these two proteins are reaction part ners. (C) 1997 Elsevier Science B.V.