Induction of luminol chemiluminescence by the manganese cluster of the photosystem II water-oxidizing complex in the S0, S1, S2, and S3 states
1996
Putrenko, I.I.
Luminol chemiluminescence (CL) (lambda max = 425 nm) induced by the manganese cluster or photosystem II (PSII) (tmax = 1-5 min) along with CL induced by mono-, di-, or tetranuclear manganese coordination complexes (tmax = 2-40 s) is observed when either 200 mM sodium phosphate or 1 M Tris-HCl + 200 micromolar EDTA are present in the reaction medium (pH 8.5) containing peroxidase. This light emission is not observed when Tris is used in the reaction medium without EDTA. The yield of a given CL without peroxidase is 5%-20% of that with peroxidase. The peroxidase-dependent CL is inhibited by catalase (I50 = 0.14-0.17 micromolar), while the peroxidase-independent CL is not inhibited by 100 mM ethanol. 1 mM NaN3, 20 micromolar Cyt c, or 0.6 micromolar catalase. The CL induced by the Mn cluster of the water-oxidizing complex (WOC) in the S3 or S2 state exceeds that of lower S states by 15-20-fold. The magnitude of CL induced by Mn complexes is dependent on the ligand type of the complex. The ligand types of the Mn complexes and the WOC in different S states are ranked according to the magnitude of the induced CL: 1,10-phenanthroline > 2,2'-bipyridine > WOC (S3 or S2) > hydrotris(pirazolyl) borate > WOC (S0-2 or S0, S1) > 1,4,7-triazacyclononane. It is concluded that CL is caused by H2O2 formed as a result of the oxidation of luminol by triplet molecular oxygen. The Mn cluster of WOC and manganese coordination complexes, acting as catalysts of this reaction, show oxidase activity. Upon S2-S3 or S1-S2 transition, changes occur in the ligand environment of the Mn cluster of WOC influencing the induction of luminol CL.
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