Studies on the mechanism of metabolic stimulation in polymorphonuclear leucocytes during phagocytosis. I. Evidence for superoxide anion involvement in the oxidation of NADPH2.

1. The oxidation of NADPH2 by leucocyte granules, as measured at acid pH in the presence of Mn-2+, was found to be inhibited by superoxide dismutase. 2. Omission of Mn-2+ markedly lowered the oxidase activity at acid pH, which was still inhibited by superoxide dismutase. 3. At alkaline pH the oxidase activity was lower than at acid pH. 4. During oxidation of NADPH2 by leucocyte granules, reduction of cytochrome c occurred which was partially inhibited by superoxide dismutase. 5. It was concluded that NADPH2 oxidation occurs through an enzymatic reaction and a nonenzymatic chain reaction. Superoxide anion (O-minus-2 and NADPH- free radical would be involved in the chain reaction. The differential sensitivity of NADPH2 oxidation to superoxide dismutase in different experimental conditions (see above 1, 2 and 3) was explained on the basis of changes in the properties of the chain reaction.