Isolation and characterization of a protein with cyanide-sensitive superoxide dismutase activity from the prokaryote, Paracoccus denitrificans.

1. A protein with cyanide-sensitive superoxide dismutase activity was isolated from the prokaryote Paracoccus denitrificans. 2. This enzyme, present in low amount in the cell, represented not more than 10% of the total cellular superoxide dismutase activity. It was obtained in a form which was 20-40-times less active than the main superoxide dismutase of P. denitrificans which is a manganese-containing enzyme. 3. It was a soluble monomeric enzyme, highly negatively charged (pI = 4.8), with an apparent molecular weight of 33,000. 4. Cyanide sensitivity was observed by NMR assay, enzyme assay and by staining the protein for superoxide dismutase activity on polyacrylamide electrophoretogram. KCN was shown to be a competitive inhibitor of this dismutase, with an inhibitor constant of 0.15 mM. 5. From the amino acid analysis, S delta Q values lower than 100 were obtained with copper-containing proteins such as the subunit II of cytochrome oxidase from P. denitrificans (69), the azurin from P. denitrificans (77), the bacteriocuprein from Photobacter leiognathi (71); with iron and manganese superoxide dismutases (40-88), and with some eukaryotic copper/zinc dismutases of fish origin (55-82).