Reconstitution of the partially purified membrane component of the superoxide‐generating NADPH oxidase of pig neutrophils with phospholipid

The NADPH‐dependent superoxide‐generating oxidase of pig neutrophils is activated by sodium dodecyl sulfate in a cell‐free system. The activation requires both membrane and cytosolic components. The membrane component was effectively extracted with 0.75% octyl glucoside and the extract was fractionated by wheat‐germagglutinin – agarose column chromatography. The chromatography resulted in loss of the O 2 − ‐generating activity in the cell‐free system. The activity, however, was restored by the reconstitution with the fraction which passed through the column (fraction A) and the one eluted with N ‐acetylglucosamine (fraction B) using an octyl glucose dilution procedure: both fractions were pre‐mixed in the presence of 0.75% octyl glucoside and diluted by putting the mixture into the detergent‐free assay mixture. The latter fraction was copurified with cytochrome b 558 , the content of which is 2.12 ± 0.53 nmol/mg protein (mean ± SD, n = 5). The potency of fraction B in the reconstitution of the O − 2 ‐generating activity was lost by heat treatment and decreased by protease treatment, whereas that of fraction A was not affected. Fraction A in the reconstitution of the O − 2 ‐generating activity was replaced by lipid extracted from fraction A, furthermore, by exogenous phospholipid, azolectin. The O − 2 ‐generating activity reconstituted with azolectin and the partially purified component in fraction B was dependent on SDS, cytosol and the concentrations of azolectin and FAD. The activity was sensitive to p ‐chloromercuribenzoate but not to azide. The maximal activity was obtained at pH 7.0–7.5. The K m values for NADPH and NADH were 0.024 mM and 0.57 mM, respectively. These properties were consistent with those of the NADPH oxidase responsible for the respiratory burst. The activity in the reconstitution system was 20.5 ± 3.5 μmol O − 2 · min −1 · mg −1 membrane‐derived protein (mean ± SD, n = 5) which shows that the membrane component was purified about 100‐fold. These findings indicate that cytochrome b 558 is probably a membrane component of the O − 2 ‐generating NADPH oxidase and its activation in the cell‐free system requires the reconstitution with phospholipids.