A novel iron protein from Desulfovibrio gigas

The isolation, purification, and partial characterization of a novel iron-containing protein from the sulfate-reducing anaerobic bacterium, Desulfovibrio gigas, is described. The highly insoluble protein was isolated from the cell debris following osmotic shock of the bacteria. The insoluble fraction consistently contained about 90% of the cell-associated iron. Elemental analysis of a crude protein preparation gave 5.3% iron, 2.9% sulfur and 11.9% nitrogen. An independent colorimetric iron analysis showed 6.4% iron. The iron could be dissociated from the protein by treatment with 5% SDS. The iron-free protein was purified by a combination of organic extraction and DEAE-cellulose chromatography. The purified protein showed only one major band, Mr 14000, by SDS-polyacrylamide gel electrophoresis. The protein could be reconstituted upon treatment with an appropriate mixture of FeS and beta-mercaptoethanol. The reconstituted protein had the same physical and chemical properties as the native protein. The amino acid composition was not unusual except for the high isoleucine content.