PURIFICATION OF A 6TH FERREDOXIN FROM RHODOBACTER-CAPSULATUS - PRIMARY STRUCTURE AND BIOCHEMICAL-PROPERTIES

A new ferredoxin has been purified from the photosynthetic bacterium R hodobacter capsulatus. It is the sixth ferredoxin to be isolated from this bacterium and it was called FdVI. Its primary structure was estab lished based on amino acid sequence analysis of the protein and of pep tides derived from it. It is composed of 106 residues including five c ysteines. The calculated mass of the polypeptide is 11402.6Da which ma tches the experimental value determined by electrospray mass spectrome try. Amino acid sequence comparison revealed that ferredoxin VI (FdVI) is strikingly similar to a ferredoxin from Caulobacter crescentus and to the putidaredoxin from Pseudomonas putida. FdVI exhibited an ultra violet-visible absorption spectrum typical for a [2Fe-2S] ferredoxin. EPR spectroscopy of the reduced protein showed a nearly axial signal s imilar to that of mitochondrial and P. putida ferredoxins. FdVI is bio synthesized in cells growing anaerobically under either nitrogen-suffi cient or nitrogen-deficient conditions. Although the function of FdVI is unknown, its structural resemblance to [2Fe-2S] ferredoxins known t o transfer electrons to oxygenases such as P-450 cytochromes, suggests that FdVI may have a similar role in R. capslatus.