Evidence that chemical modification of a positively charged residue at position 189 causes the loss of catalytic activity of iron-containing and manganese-containing superoxide dismutases

Abstract

The Escherichia coli, Bacillus stearothermophilus, and human manganese-containing superoxide dismutases (MnSODs) and the E. coli iron-containing superoxide dismutase (FeSOD) are extensively inactivated by treatment with phenylglyoxal, an arginine-specific reagent. Arg-189, the only conserved arginine in the primary sequences of these four enzymes, is also conserved in the three additional FeSODs and five of the six additional MnSODs sequenced to date. The only exception is Saccharomyces cerevisiae MnSOD, in which it is conservatively replaced by lysine. Treatment of S. cerevisiae MnSOD with phenylglyoxal under the same conditions used for the other SODs gives very little inactivation. However, treatment with low levels of 2,4,6-trinitrobenzenesulfonate (TNBS) or acetic anhydride, two lysine-selective reagents that cause a maximum of 60-80% inactivation of the other four SODs, gives complete inactivation of the yeast enzyme. Total inactivation of yeast MnSOD with TNBS correlates with the modification of approximately five lysines per subunit, whereas six to seven acetyl groups per subunit are incorporated on complete inactivation with [14C]-acetic anhydride. It appears that the positive charge contributed by residue 189, lysine in yeast MnSOD and arginine in all other SODs, is critical for the catalytic function of MnSODs and FeSODs.