Activation by gamma interferon of human macrophage capability to produce toxic oxygen molecules is accompanied by decreased Km of the superoxide-generating NADPH oxidase.

Capability to release superoxide anion in response to phorbol myristate acetate by intact cells has been compared with Kinetic properties of NADPH oxidase by lysates of human monocytes and monocyte-derived macrophages. Maturation of monocytes in vitro is accompanied by substantial decrease of the capability to release superoxide anion in response to phorbol myristate acetate. Exposure of mature macrophages to recombinant interferon gamma enhances respiratory burst activity up to 3-4 fold. Modifications of NADPH oxidase accompany changes in the ability to release superoxide anion. The affinity of the oxidase for its substrate is higher in monocytes and gamma interferon treated macrophages, while Vmax is not changed.