Regulation of the human leukocyte 5-lipoxygenase: stimulation by micromolar Ca2+ levels and phosphatidylcholine vesicles.
Human leukocyte 5-lipoxygenase (EC 1.13.11.12) is unique among the human lipoxygenase not only in its requirement for free ionized calcium, but also in its regulation by a membrane-associated stimulatory factor, the 100,000 x g pellet. In the present study, phosphatidylcholine (PC) vesicles, in the absence of 100,000 x g pellet, exhibited a dose-dependent stimulatory activity on the 5-lipoxygenase, which was at least as effective as the 100,000 x g pellet. Furthermore, the enzyme was activated by isolated human neutrophil plasma membranes and to a lesser degree by endoplasmic reticulum. The chemoattractant peptide fMet-Leu-Phe (0.1 microM), GTP (10 microM), toxin from bacterium Bordetella pertussis (islet activating protein, 5 micrograms/ml) and their various combinations were unable to modulate the enzymatic activity of the 5-lipoxygenase. Stimulation of the 5-lipoxygenase by relatively low levels of free ionized calcium was observed both in the presence of the pellet and PC vesicles: maximal stimulation was seen at about 10 microM Ca2+. The human leukocyte leukotriene A4 synthase activity also exhibited a similar requirement for free calcium ions. The present study indicates that the membrane-associated stimulatory factor of the human leukocyte 5-lipoxygenase may be replaced by PC vesicles. Moreover, the 5-lipoxygenase and leukotriene A4 synthase activities require significantly lower Ca2+ levels for maximal activation than has been reported previously.
Puustinen
T
T
Department of Physiological Chemistry, Karolinska Institutet, Stockholm, Sweden.
Scheffer
M M
MM
Samuelsson
B
B
D001094:Arachidonate 5-Lipoxygenase / Q000097:blood*; D001091:Arachidonate Lipoxygenases / Q000097:blood*; D002118:Calcium / Q000494:pharmacology*; D002462:Cell Membrane / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D007962:Leukocytes / Q000201:enzymology*; D016859:Lipoxygenase Inhibitors; D008565:Membrane Proteins / Q000502:physiology; D010713:Phosphatidylcholines / Q000502:physiology*
D016859:Lipoxygenase Inhibitors; D008565:Membrane Proteins; D010713:Phosphatidylcholines; D001091:Arachidonate Lipoxygenases; D001094:Arachidonate 5-Lipoxygenase; D002118:Calcium