Merged Heme and Non-Heme Manganese Cofactors for a Dual Antioxidant Surveillance in Photosynthetic Organisms

The coupling of a polycationic Mn(III)-porphyrin, with a dinuclear Mn-2(11,II)L-2 core (HL = 2-{[[di(2-pyridyl)methyl](methyl)amino]methyl}phenol), results in a dual Superoxide Dismutase (SOD) and Catalase (CAT) functional analogue, Mn2L2 Pn+,, enabling a detoxification cascade of the superoxide anion and hydrogen peroxide into benign H2O and O-2. The SOD/CAT artificial manifolds, joined in one asset, exhibit a peak catalytic performance under physiological conditions, with log k(cat)(O-2(center dot-)) >= 7 and k(cat)(H2O2)/K-m = 1890. The dual-enzyme (dizyme) concept allows for a builtin self-protection against the irreversible bleaching of the porphyrin unit (>75% protection), readily induced by H2O2 (200 mu M, 20 equiv, in buffer solution, pH 7.8). We show herein that incubation of the photosynthetic green algae, Chlamydomonas reinhardtii, with the synthetic dizyme (as low as 0.1 mu M), prevents H2O2 accumulation under high-light illumination conditions, thus providing antioxidant surveillance and photoprotection.