Iron Uroporphyrin I and a Heme c-Derivative Are Prosthetic Groups in Desulfovibrio gigas Rubredoxin Oxidase1

Rubredoxin-oxygen oxidoreductase (ROO) from the sulfate-reducing bacterium Desulfovibrio gigas, is an unusual terminal oxidase capable of reducing molecular O2 to water. The nature of its heme prosthetic groups has been investigated. It was found to contain two distinct hemes. One is Fe uroporphyrin I. The second is closely related to heme c. It is an Fe protoporphyrin IX where two electrophilic groups have added covalently across the double-bonds of the former 3,8 vinyl groups (IUB-IUPAC Tetrapyrrole numbering). These covalent attachment bonds are not to the main polypeptide chain, but instead are to an unidentified component. This component is soluble in acidic acetone, but cannot be extracted into organic solvents that typically solubilize free heme groups. Preliminary evidence suggests that the covalent bonds are not thioether bonds, but they are acid labile.