The effect of receptor-mediated stimulation on the translocation of 5-lipoxygenase

It has been shown that calcium ionophore-mediated activation of the 5-lipoxygenase is followed by an extensive loss of enzyme activity. We investigated whether IgE/antigen stimulation of mast cells leads to a similar inactivation. This challenge caused a minor loss of 5-lipoxygenase activity as compared to A23187. Both stimuli resulted in the synthesis of similar amounts of leukotrienes. Immunoblot experiments showed that after antigen, the membrane association of the enzyme was reversible. In contrast, with A23187 translocation continued during the time of observation (60 min). Calcium chelators, added after A23187 stimulation, stopped the enzyme inactivation and reversed the membrane binding. The data suggest that the continuous, high intracellular calcium levels initiated by A23187 inactivate the enzyme, while the transient increase in calcium during receptor-mediated stimulation is sufficient to activate the 5-lipoxygenase but not to extensively inactivate it.