Synthesis and kinetic evaluation of a trifunctional enzyme mimic with a dimanganese active centre.

Glutathione peroxidase (GPX), superoxide dismutase (SOD) and catalase (CAT) play crucial roles in the metabolism and homeostasis of reactive oxygen species (ROS) in living organisms. From examination of the steady state and pre-steady state kinetic behavior of natural GPX it was found that, in contrast to accepted theories, the affinity of the enzyme for H(2)O(2) rather than reduced glutathione (GSH) most significantly affects its kinetic behavior. Consequently, an enzyme mimic was produced with a similar affinity for the substrate H(2)O(2). A salicylaldehyde Schiff base containing a dimanganese centre was selected as a precursor, because it has high H(2)O(2)-binding affinity for such a relatively small molecule and similar catalytic activity to that of SOD and CAT. Selenium was also incorporated into the catalytic center to provide activity similar to that of GPX, and thus trifunctional enzymatic activity. The K(mH2O2) of the mimic (7.32×10(-2) mM) was found quite close to that of natural enzyme (1.0×10(-2) mM), indicating that the affinity of the mimic to H(2)O(2) was successfully increased to approach natural GPX. The steady state kinetic performance of the enzyme mimic showed that the ratio between k(cat)/K(mGSH) and k(cat)/ K(mH2O2) was quite similar to that of native GPX, indicating that the Mn(III)(2)(L-Se-SO(3)Na) had the same selectivity for both substrates GSH and H(2)O(2) as native GPX, which put it among the best existing GPX mimics. Moreover, the new mimic was confirmed to strongly inhibit lipid peroxidation and mitochondrial swelling, probably due to the synergism between the three antioxidant enzymatic activities.