(B) Redox cycling of redox-active compounds through one-electron reduction. (A) 9,10-PQ, 9,10-phenanthrenequinone PQQ, pyrroloquinoline quinone DDP, cis-9,10-dihydroxy-9,10-dihydrophenanthrene. 4)įig. 1. Structures of Chemicals Used in This Study (A) and Schematic Procedure for the BPM-Labeling Assay to Detect Redox-Active Compounds (B, C) 3) PQQ also acts as an efficient electron transfer catalyst from reducing agents such as NADPH to O 2 to yield ROS. − is also produced by a chemical disproportionation reaction between 9,10-PQ and 9,10-dihydroxyphenanthrene, a two-electron reductant of 9,10-PQ, that is catalyzed by NADPH-dependent reductases such as aldo-keto reductases or NADPH:quinone oxidoreductase 1 to produce excessive ROS in cells.−), which readily reacts with molecular oxygen (O 2) to yield superoxide and hydrogen peroxide (H 2O 2) 3) ( Fig.We reported previously that 9,10-PQ undergoes one-electron reduction with dithiol compounds or reduced nicotinamide adenine dinucleotide phosphate (NADPH) to form its intermediate semiquinone radical (9,10-PQ 2) Once these substances are incorporated into cells, they interact with biological electron donors to undergo redox cycling, thereby generating reactive oxygen species (ROS). 1A) is contained in various dietary sources. 1A) is found as a contaminant in diesel exhaust particles (DEP) and particulate matter 2.5, 1) while pyrroloquinoline quinone (PQQ, Fig. For example, 9,10-phenanthrenequinone (9,10-PQ, Fig. These results suggest that the developed assay is useful for the detection of S-oxidation of proteins.ĭuring our lifetime, we are exposed to various electron acceptors present in the environment and our diet. S-Oxidation of proteins in a mouse liver supernatant was detected during reaction of 9,10-PQ or PQQ with electron donors such as dithiothreitol or reduced nicotinamide adenine dinucleotide phosphate (NADPH), whereas cellular protein oxidation was not observed in the absence of electron donors. ![]() In the present study, we developed a convenient assay based on a combination of an enzyme-linked immunosorbent assay and a biotin-PEAC 5-maleimide assay and used it to determine protein S-oxidation by ROS during redox cycling of 9,10-phenanthrenequinone (9,10-PQ) and pyrroloquinoline quinone (PQQ). Hydrogen peroxide (H 2O 2) causes S-oxidation of proteins and is associated with activation of the redox signaling pathway and/or toxicity ( Chem. Redox-active quinones generate reactive oxygen species (ROS) through their redox cycling with electron donors.
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