title: Reversible, calcium-dependent membrane association of human leukocyte 5-lipoxygenase.
abstract: Maximal activity of human leukocyte 5-lipoxygenase requires Ca2+, ATP, a microsomal membrane preparation, and two cytosolic stimulatory factors. We report here some effects of Ca2+ on the physical properties of the 5-lipoxygenase. When leukocytes were homogenized in the presence of 2 mM EDTA, 5-lipoxygenase was found to be a soluble enzyme. However, when Ca2+ was added to homogenization buffers at 0-1 mM in excess of EDTA, increasing quantities of the enzyme were recovered in the microsomal membrane fraction (100,000 X g pellet). The membrane-associated enzyme was resolubilized by washing pellet preparations in buffers containing 2 mM EDTA and was partially purified by anion-exchange chromatography. Studies of the stimulatory-factor requirements of the membrane-associated, resolubilized, and partially purified enzyme indicated that one of the cytosolic 5-lipoxygenase stimulatory factors exhibited a reversible, Ca2+-dependent membrane association, similar to that of the enzyme itself. Ca2+ also caused a destabilization of the 5-lipoxygenase. Homogenates prepared in the presence of Ca2+ contained lower total enzyme activity, and retention of activity in these samples over time was also diminished.
mesh_terms: D001094:Arachidonate 5-Lipoxygenase / Q000097:blood* / Q000302:isolation & purification; D001091:Arachidonate Lipoxygenases / Q000097:blood*; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D002462:Cell Membrane / Q000201:enzymology; D002851:Chromatography, High Pressure Liquid; D002852:Chromatography, Ion Exchange; D006801:Humans; D007700:Kinetics; D007962:Leukocytes / Q000201:enzymology*
chemical_list: D000001:Calcimycin; D001091:Arachidonate Lipoxygenases; D001094:Arachidonate 5-Lipoxygenase; D002118:Calcium