Characterization of the membrane-associated GTPase activity: effects of chemotactic factors and toxins.

Membranes prepared from rabbit neutrophils exhibit GTPase activity which can be stimulated by the chemotactic factor fMet-Leu-Phe. The maximum contribution of the ATPase activities to the basal and the fMet-Leu-Phe-stimulated GTPase activities are less than 20% and 9%, respectively. The basal GTPase activity has a Vmax = 34.2 +/- 1.3 (pmol/mg protein, min) and a Km = 0.39 +/- 0.03 microM; and the fMet-Leu-Phe-stimulated has a Vmax = 52.3 +/- 2.5 (pmol/mg protein, min), and a Km = 0.29 +/- 0.02 microM. The GTPase activity can be stimulated by fMet-Leu-Phe and leukotriene B4. Unlike these two chemotactic factors, concanavalin A does not stimulate this GTPase activity. In addition, the rise in intracellular concentration of free calcium produced by concanavalin A is not inhibited by pertussis toxin treatment. Both the basal and stimulated GTPase activities are affected by pertussis toxin, cholera toxin and N-ethylmaleimide.