Reversible translocation of 5-lipoxygenase in mast cells upon IgE/antigen stimulation.

The 5-lipoxygenase catalyzes the first two steps in the metabolism of arachidonic acid to leukotrienes. It has been shown that the calcium influx into leukocytes following stimulation by A23187 activates the enzyme and causes its translocation to the membrane. Leukotrienes are formed, and then the enzyme seems to be irreversibly inactivated. In the present investigation we have compared the effect of receptor-mediated mast cell activation (IgE/antigen) and A23187 on 5-lipoxygenase activity and translocation to the membrane. In contrast to the ionophore, IgE/antigen, which initiated the formation of similar amounts of leukotrienes as A23187, caused minor inactivation of the enzyme. Immunoblot analysis demonstrated that after antigen the membrane association of the 5-lipoxygenase was reversible, while with A23187 the translocation continued during the time of observation (60 min). Addition of a calcium chelator after ionophore challenge, prevented further inactivation of the enzyme and reversed its membrane binding. The data suggest that the continuous influx of calcium with A23187 is responsible for the extensive inactivation of the 5-lipoxygenase. In contrast, during receptor-mediated stimulation the transient increase in intracellular calcium seems to conserve the enzyme activity.