Superoxide dismutases catalyze the decomposition of the superoxide radical, thus protecting aerobes from this radical and other cytotoxic species formed during the reduction of oxygen to water. There are three forms of superoxide dismutases: manganese-, iron-, and copper-and zinc-containing enzymes. Prokaryotes contain manganese or iron dismutases, or both. Copper-zinc dismutases are found in most erkaryote cytosols; eukaryote organelles contain the manganese enzyme. Why do certain species contain a certain type(s) of superoxide dismutase and other species another type(s)? The long range goal of this project is to identify the structural and the chemical properties of the three dismutase forms which make them particularly suited for the species and intracellular location in which they reside. During the coming budget year (May, 1981, through April, 1982) covalent structural analysis will continue to be the central experimental approach and the principal means of comparing superoxide dismutases. The bacteriocuprein from a symbiotic strain of Photobacterium leiognathi has been purified, by modifications of published methods. Additional quantities of the homogenous protein will be prepared, then peptide mapping and partial amino acid sequence analysis will be undertaken, to compare this unusual bacterial dismutase with copper-zinc dismutases from eukaryotes. Other strains of P. Leiognathi will be screened for bacteriocuprein. (These strains will be obtained from Dr. Kenneth Nealson of Scripps Institute of Oceanography and Dr. James Morin of UCLA Biology Department.) If time allows, the purification of the bacteriocuprein from Paracoccus denitrificans may be undertaken. Peptide isolations and sequence determination with the mitochondrial (manganese-containing) superoxide dismutase from chicken liver, commenced during the past budget year, will be continued in the coming 12 months.