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

1. 1. The oxidation of NADPH₂ by leucocyte granules, as measured at acid pH in the presence of Mn²⁺, was found to be inhibited by superoxide dismutase. 2. 2. Omission of Mn²⁺ markedly lowered the oxidase activity at acid pH, which was still inhibited by superoxide dismutase. 3. 3. At alkaline pH the oxidase activity was lower than at acid pH, Mn²⁺ had no stimulatory effect and superoxide dismutase was less inhibitory than at acid pH. 4. 4. During oxidation of NADPH₂ by leucocyte granules, reduction of cytochrome c occurred which was partially inhibited by superoxide dismutase. 5. 5. It was concluded that NADPH₂ oxidation occurs through an enzymatic reaction and a nonenzymatic chain reaction. Superoxide anion (O₂ ^- 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.