The voltage dependence of NADPH oxidase reveals why phagocytes need proton channels.
The enzyme NADPH oxidase in phagocytes is important in the body's defence against microbes: it produces superoxide anions (O2-, precursors to bactericidal reactive oxygen species). Electrons move from intracellular NADPH, across a chain comprising FAD (flavin adenine dinucleotide) and two haems, to reduce extracellular O2 to O2-. NADPH oxidase is electrogenic, generating electron current (I(e)) that is measurable under voltage-clamp conditions. Here we report the complete current-voltage relationship of NADPH oxidase, the first such measurement of a plasma membrane electron transporter. We find that I(e) is voltage-independent from -100 mV to >0 mV, but is steeply inhibited by further depolarization, and is abolished at about +190 mV. It was proposed that H+ efflux mediated by voltage-gated proton channels compensates I(e), because Zn2+ and Cd2+ inhibit both H+ currents and O2- production. Here we show that COS-7 cells transfected with four NADPH oxidase components, but lacking H+ channels, produce O2- in the presence of Zn2+ concentrations that inhibit O2- production in neutrophils and eosinophils. Zn2+ does not inhibit NADPH oxidase directly, but through effects on H+ channels. H+ channels optimize NADPH oxidase function by preventing membrane depolarization to inhibitory voltages.
DeCoursey
Thomas E
TE
Department of Molecular Biophysics and Physiology, Rush Presbyterian St Luke's Medical Center, 1750 West Harrison, Chicago, Illinois 60612, USA. tdecours@rush.edu
Morgan
Deri
D
Cherny
Vladimir V
VV
D000818:Animals; D019556:COS Cells; D002104:Cadmium / Q000378:metabolism; D004594:Electrophysiology; D004789:Enzyme Activation; D004804:Eosinophils / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D006801:Humans; D051379:Mice; D019255:NADPH Oxidases / Q000235:genetics / Q000378:metabolism*; D009504:Neutrophils / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D010586:Phagocytes / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism*; D017494:Proton Pumps / Q000378:metabolism*; D011522:Protons; D013481:Superoxides / Q000378:metabolism; D015032:Zinc / Q000378:metabolism / Q000494:pharmacology
D017494:Proton Pumps; D011522:Protons; D002104:Cadmium; D013481:Superoxides; D019255:NADPH Oxidases; D015032:Zinc