DIFFERENTIAL EXPRESSION OF SUPEROXIDE DISMUTASES CONTAINING NI AND FEZN IN STREPTOMYCES-COELICOLOR/

Streptomyces coelicolor contains two distinct superoxide dismutase (SO D) activities detected on native PAGE. The level of each changed diffe rently depending on growth media and scarcely responded to paraquat, a superoxide-generating agent. The total SOD activity doubled in late e xponential phase compared with that in mid-exponential phase and less than double upon treatment with plumbagin, another superoxide-generati ng agent. The two SODs from S. coelicolor ATCC 10147 (Muller) strain w ere purified to near homogeneity. SOD1, a tetramer of 13.4-kDa subunit s, was found to be a novel type of SOD containing 0.74 mel nickel/mol subunit as determined by atomic absorption spectroscopy. SOD2, a tetra mer of 22.2-kDa subunits, was found to contain 0.36 mol iron and 0.26 mol zinc/mol subunit. The N-terminal amino acid sequences of both SODs were determined. SOD2 is similar to manganese-containing superoxide d ismutases (MnSODs) and iron-containing superoxide dismutases (FeSODs) from other organisms, whereas SOD1 is less similar to known SODs but s till contains a few conserved amino acids, The effects of metals and c helating agents on the expression of these two SODs were examined. The presence of nickel at micromolar concentrations in growth media induc ed the expression of SOD1 (nickel-containing superoxide dismutase: NiS OD), whereas the expression of SOD2 (iron/zinc-containing superoxide d ismutase; FeZnSOD) was repressed. The changes in SOD activities were p ositively correlated with the amount of each enzyme as determined by i mmunoblotting. suggesting that metals do not modulate the activity per se but the amount of each protein.