Mg2+ activates 5-lipoxygenase in vitro: Dependency on concentrations of phosphatidylcholine and arachidonic acid

Mg2+ gave dose-dependent activation of 5-lipoxygenase (5LO) in vitro. As fo r Ca2+, the activation-depended on the presence of phosphatidylcholine (PC) vesicles, and the activation response was different at various combination s of arachidonate and PC. Stimulation of 5LO activity was observed with Mg2 + concentrations of 0.1-1 mM, similar to the concentration range of free Mg 2+ in mammalian cells. However, to observe a clear increase in 5LO hydropho bicity, a higher concentration of Mg2+ (4 mM) was required, and at this con centration also 5LO activation was optimal. Combinations of Mg2+ with ATP ( containing free Mg2+ and MgATP(2-) complex) gave better activation of 5LO t han either agent alone. This effect of Mg2+ (and ATP) could be of interest in relation to basal 5LO activity in cells not subjected to a particular st imulus.