Studies on the granulocyte plasma membrane oxidase

Abstract

The plasma membrane of granulocytes contains an oxidase which catalyses reduction of oxygen to superoxide. With phagocytosis, this oxidase is incorporated into the phagocytic vacuole membrane, facilitating the delivery of cytotoxic superoxide to the ingested micro-organism. We have examined the role of cytoplasmic microtubules (MT) and microfilaments (MF) in the control of the activity of this plasma membrane enzyme. These studies were prompted by reports showing that MT and MF control many plasma membrane phenomena, including the movement of proteins within the plane of the membrane and the topographical organization of the plasma membrane during phagocytosis. These experiments were designed to record changes in the initial rate of oxidase activity after treatment of intact granulocytes with drugs known to disrupt MF (cytochalasin B) or MT (colchicine, vinblastine, vincristine). Control experiments showed that MT and MF were indeed disrupted by these drug treatments. MF disruption produced an enhancement in oxidase activity whereas MT disruption resulted in inhibition except when very low doses of, or brief exposures to the agents were used, when a paradoxical stimulation was seen. Correlative electron microscopic studies showed the sites of oxidase activity to the homogeneously distributed on the surface of untreated, but not drug-treated granulocytes. It was concluded that MF may provide a constraint against plasma membrane oxidase activity. Conversely, MT presumably by controlling the topographical organization of the membrane, seem to be required for plasma membrane oxidase activity. These findings may have some relevance in vivo in that inhibition of the crucial granulocyte plasma membrane oxidase activity may partially explain the increased risk of infection in cancer patients treated with the vinca alkaloids.