Oxidation-reduction properties of the cytochrome b found in the plasma-membrane fraction of human neutrophils. A possible oxidase in the respiratory burst.
The oxidation-reduction midpoint potential of the cytochrome b found in the plasma membrane of human neutrophils has been determined at pH 7.0 (Em,7.0) from measurements of absorption spectra at fixed potentials. In both unstimulated and phorbol myristate acetate-stimulated cells Em,7.0 was -245 mV. Changes in pH affected the Em of the cytochrome b, with a slope of approx. 25 mV/pH unit change. The Em,7.0 of the haem group(s) of the membrane-bound myeloperoxidase of human neutrophils was found to be +34 mV. The plasma membranes contained no detectable ubiquinone, and no iron-sulphur compounds were detected by e.p.r. spectroscopy at 5-20 K. No flavins were detected by e.p.r. spectroscopy. The cytochrome b-245 was not reduced by added NADH or NADPH. Dithionite-reduced cytochrome b-245 formed a complex with CO, supplied as a saturated solution, which was dissociated with 26 microseconds illumination from a xenon flash lamp, and the recombination with CO had a half-time of approx. 6 ms. Partly (80%) reduced cytochrome b-245 was oxidized by added air-saturated buffer with a half-time faster than 1 s at 20 degrees C, a resolution limited by mixing time. These results are compatible with cytochrome b-245 acting as an oxidase.
D002462:Cell Membrane / Q000378:metabolism; D003573:Cytochrome b Group; D003580:Cytochromes / Q000097:blood* / Q000378:metabolism; D004579:Electron Transport; D006801:Humans; D066298:In Vitro Techniques; D009504:Neutrophils / Q000201:enzymology / Q000378:metabolism*; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000097:blood*; D010782:Photolysis; D011199:Potentiometry; D013053:Spectrophotometry
D003573:Cytochrome b Group; D003580:Cytochromes; D010088:Oxidoreductases