Factors affecting the catalytic activity of Mn-catalase mimics

DAIER, VERÓNICA; CLAUDIA PALOPOLI,; HERNÁN BIAVA,; DIEGO MORENO,; SANDRA SIGNORELLA,

BIOCELL

INST HISTOL EMBRIOL-CONICET

Año: 2005 vol. 29 p. 121 - 121

0327-9545

Manganese catalases (MnCAT) possess a diMn active site and disproportionate H2O2 by cycling between the MnII2 and MnIII2 oxidation states. The crystal structure of MnCaT from L. plantarum and T. thermophilus reveal that the two Mn ions are triply bridged through a carboxylate from a glutamate residue and two solvent- derived single atom bridges. A wide variety of diMn complexes have been synthesized to mimic structural features of MnCAT, but they are 103-104 times slower than the enzyme. The obtention of more effective mimics of MnCAT requires a better understanding of the factors controlling their catalytic activity. With this in mind, we have evaluated the catalase-like activity of a family of Mn complexes with salpentOH (1,5-bis(salicylidenamino)pentan-3-ol) and its phenyl-ring substituted derivatives: [Mn 2(μ-OAc)(μ- OMe)X-salpentO (MeOH) 2 ]Br. These complexes are good structural mimics of the MnIII2 form of MnCAT (with Mn···Mn separation only 0.1-0.2 Å shorter than found for the enzyme), disproportionate more than 1000 eq. of H 2O 2 with saturation kinetics, and show substrate affinity comparable to that of the biosite. Unlike other complexes with similar geometry, atomic environment and redox potentials, but longer intermetallic separation, which cycle between the MnII2/MnIII2 levels, complexes of the X-salpentOH family cycle between MnIII2/MnIV2. Thus, the Mn···Mn distance is an important factor in these reactions: the short Mn···Mn separation (~2.93 Å) imposed by the ligand in the X- salpentOH models seems to be best suited for accommodating the higher oxidation states of Mn.