In vivo incorporation of copper into the iron‐exchangeable and manganese‐exchangable superoxide dismutase from Propionibacterium shermanii

Propionibacterium shermanii , an aerotolerant anaerobe, produces an iron‐containing or a manganese‐containing superoxide dismutase, depending on the metal supplied in the culture medium [Meier, B., Barra, D., Bossa, F., Calabrese, L. & Rotilio, G. (1982) J. Biol. Chem. 257 , 13977–13980]. In this study, we demostrate in vivo incorporation of copper into an active superoxide‐dismutase protein when iron and manganese are absent from the growth medium. Superoxide dismutases containing either iron, manganese or copper were isolated from P. shermanii , their complete amino acid sequences were determined and the identity of their protein moieties was established. The polypeptide chain is made up of 201 amino acid residues, corresponding to a molecular mass of 22.6 kDa. From sedimentation equilibrium experiments, the native protein shows a molecular mass of approximately 86 kDa and therefore consists of four identical subunits. The primary structure was compared with the structure of other Fe‐superoxide dismutases and Mn‐superoxide dismutases, in particular those possessing a strict metal cofactor specificity.