H2S oxidation by nanodisc-embedded human sulfide quinone oxidoreductase.

摘要: Buildup of hydrogen sulfide (H2S), which functions as a signaling molecule but is toxic at high concentrations, averted by its efficient oxidation the mitochondrial pathway. The first step in this pathway catalyzed flavoprotein, quinone oxidoreductase (SQR), converts H2S to persulfide and transfers electrons coenzyme Q via flavin cofactor. All previous studies on human SQR have used detergent-solubilized protein. Here, we embedded nanodiscs (ndSQR) studied highly homogenous preparations steady-state rapid-kinetics techniques. ndSQR exhibited higher catalytic rates membranous environment than solubilized state. Stopped-flow spectroscopic data revealed that transfer sulfane sulfur from an SQR-bound cysteine intermediate small-molecule acceptor rate-limiting step. physiological has been subject controversy; report kinetic analysis consistent with glutathione rather sulfite being predominant physiologically relevant concentrations respective metabolites. identity important bearing how organized. Our are more reaction sequence for being: → sulfate, convoluted route would result if were primary sulfur. In summary, nanodisc-incorporated exhibits enhanced performance, pre-steady-state kinetics characterization complete cycle indicates GSH serves acceptor.