The oxidized (3,3) state of manganese catalase. Comparison of enzymes fromThermus thermophilus and Lactobacillus plantarum

Manganese catalases contain a binuclear manganese cluster that catalyzes th e redox dismutation of hydrogen peroxide, interconverting between dimangane se(II) [(2,2)] and dimanganese(III) [(3,3)] oxidation states during turnove r. We have investigated the oxidized (3,3) states of the homologous enzymes from Thermus thermophilus and Lactobacillus plantarum using a combination of optical absorption, CD, MCD, and EPR spectroscopies as sensitive probes of the electronic structure and protein environment for: the active site me tal clusters. Comparison of results for these two enzymes allows the essent ial features of the active sites to be recognized and the differences ident ified. For both enzymes, preparations having the highest catalytic activity have diamagnetic ground states, consistent with the bis-mu-bridging dimang anese core structure that has been defined crystallographically. Oxidative damage and exogenous ligand binding perturb the core structure of LPC, conv erting the enzyme to a distinct form in which the cluster becomes paramagne tic as a result of altered exchange coupling mediated by the bridging ligan ds. The TTC cluster does not exhibit this sensitivity to ligand binding; im plying a different reactivity for the bridges in that enzyme. A mechanism i s proposed involving distinct coordination modes for peroxide substrate in each of the two half-reactions for enzyme turnover.