Catalyzes the oxygenation of arachidonate ((5Z,8Z,11Z,14Z)-eicosatetraenoate) to 5-hydroperoxyeicosatetraenoate (5-HPETE) followed by the dehydration to 5,6- epoxyeicosatetraenoate (Leukotriene A4/LTA4), the first two steps in the biosynthesis of leukotrienes, which are potent mediators of inflammation (PubMed:8631361, PubMed:21233389, PubMed:22516296, PubMed:24282679, PubMed:19022417, PubMed:23246375, PubMed:8615788, PubMed:24893149, PubMed:31664810). Also catalyzes the oxygenation of arachidonate into 8-hydroperoxyicosatetraenoate (8-HPETE) and 12-hydroperoxyicosatetraenoate (12-HPETE) (PubMed:23246375). Displays lipoxin synthase activity being able to convert (15S)-HETE into a conjugate tetraene (PubMed:31664810). Although arachidonate is the preferred substrate, this enzyme can also metabolize oxidized fatty acids derived from arachidonate such as (15S)-HETE, eicosapentaenoate (EPA) such as (18R)- and (18S)-HEPE or docosahexaenoate (DHA) which lead to the formation of specialized pro-resolving mediators (SPM) lipoxin and resolvins E and D respectively, therefore it participates in anti-inflammatory responses (PubMed:21206090, PubMed:31664810, PubMed:8615788, PubMed:17114001, PubMed:32404334). Oxidation of DHA directly inhibits endothelial cell proliferation and sprouting angiogenesis via peroxisome proliferator-activated receptor gamma (PPARgamma) (By similarity). It does not catalyze the oxygenation of linoleic acid and does not convert (5S)-HETE to lipoxin isomers (PubMed:31664810). In addition to inflammatory processes, it participates in dendritic cell migration, wound healing through an antioxidant mechanism based on heme oxygenase-1 (HO-1) regulation expression, monocyte adhesion to the endothelium via ITGAM expression on monocytes (By similarity). Moreover, it helps establish an adaptive humoral immunity by regulating primary resting B cells and follicular helper T cells and participates in the CD40-induced production of reactive oxygen species (ROS) after CD40 ligation in B cells through interaction with PIK3R1 that bridges ALOX5 with CD40 (PubMed:21200133). May also play a role in glucose homeostasis, regulation of insulin secretion and palmitic acid-induced insulin resistance via AMPK (By similarity). Can regulate bone mineralization and fat cell differentiation increases in induced pluripotent stem cells (By similarity). (5Z,8Z,11Z,14Z)-eicosatetraenoate + O2 = H2O + leukotriene A4 18-HEPE + O2 = (5S)-hydroperoxy-18-hydroxy-(7E,9E,11Z,14Z,16E)-eicosapentaenoate (18R)-hydroxy-(5Z,8Z,11Z,14Z,16E)-eicosapentaenoate + O2 = (5S)-hydroperoxy-(18R)-hydroxy-(6E,8Z,11Z,14Z,16E)-eicosapentaenoate (18S)-hydroxy-(5Z,8Z,11Z,14Z,16E)-eicosapentaenoate + O2 = (5S)-hydroperoxy-(18S)-hydroxy-(6E,8Z,11Z,14Z,16E)-eicosapentaenoate (5S)-hydroperoxy-(18S)-hydroxy-(6E,8Z,11Z,14Z,16E)-eicosapentaenoate = (5S,6S)-epoxy-(18S)-hydroxy-(7E,9E,11Z,14Z,16E)-eicosapentaenoate + H2O (5S)-hydroperoxy-(18R)-hydroxy-(6E,8Z,11Z,14Z,16E)-eicosapentaenoate = (5S,6S)-epoxy-(18R)-hydroxy-(7E,9E,11Z,14Z,16E)-eicosapentaenoate + H2O (5S)-hydroperoxy-18-hydroxy-(7E,9E,11Z,14Z,16E)-eicosapentaenoate = (5S,6S)-epoxy-18-hydroxy-(7E,9E,11Z,14Z,16E)-eicosapentaenoate + H2O (5Z,8Z,11Z,14Z)-eicosatetraenoate + O2 = (5S)-hydroperoxy-(6E,8Z,11Z,14Z)-eicosatetraenoate (5Z,8Z,11Z,13E,15S)-hydroxyeicosatetraenoate + O2 = (5S)-hydroperoxy-(15S)-hydroxy-(6E,8Z,11Z,13E)-eicosatetraenoate (5S)-hydroperoxy-(6E,8Z,11Z,14Z)-eicosatetraenoate = H2O + leukotriene A4 (5Z,8Z,11Z,14Z)-eicosatetraenoate + O2 = (8S)-hydroperoxy-(5Z,9E,11Z,14Z)-eicosatetraenoate (5Z,8Z,11Z,14Z)-eicosatetraenoate + O2 = (12S)-hydroperoxy-(5Z,8Z,10E,14Z)-eicosatetraenoate (5Z,8Z)-eicosadienoate + O2 = (5S)-hydroperoxy-(6E,8Z)-eicosadienoate (12S)-hydroxy-(5Z,8Z,10E,14Z)-eicosatetraenoate + O2 = (5S)-hydroperoxy-(12S)-hydroxy-(6E,8Z,10E,14Z)-eicosatetraenoate (5Z,8Z,11Z,14Z,17Z)-eicosapentaenoate + O2 = 5-hydroperoxy-(6E,8Z,11Z,14Z,17Z)-eicosapentaenoate (4Z,7Z,10Z,13Z,16Z,19Z)-docosahexaenoate + O2 = (14S)-hydroperoxy-(4Z,7Z,10Z,12E,16Z,19Z)-docosahexaenoate (4Z,7Z,10Z,13Z,16Z,19Z)-docosahexaenoate + O2 = (7S)-hydroperoxy-(4Z,8E,10Z,13Z,16Z,19Z)-docosahexaenoate (4Z,7Z,10Z,13Z,16Z,19Z)-docosahexaenoate + O2 = (17S)-hydroperoxy-(4Z,7Z,10Z,13Z,15E,19Z)-docosahexaenoate Binds 1 Fe cation per subunit. Undergoes a sequential loss of the oxygenase and pseudoperoxidase activities which is dependent on the structural characteristics of the substrate for the reaction, on oxygen concentration and on exposure to phospholipids and calcium (PubMed:8631361). 15-HETE and other 15-mono-hydroxyeicosanoids exhibit the highest inhibitory potencies in their capability of suppressing 5-lipoxygenation of arachidonic acid, whereas the other HETEs, (5S,15S)-dihydroxy-(6E,8Z,11Z,13E)-eicosatetraenoic acid (5,15-diHETE) as well as octadecanoids, are modest or poor inhibitors (PubMed:8615788). The formation of (5S)-hydroperoxy-(15S)-hydroxy-(6E,8Z,11Z,13E)-eicosatetraenoate is strongly stimulated by either hydroperoxypolyenoic fatty acids or arachidonic acid (PubMed:8615788). Arachidonate 5-lipoxygenase and leukotriene A4 synthase activities are allosterically increased by ATP (PubMed:24893149). Lipid metabolism; leukotriene A4 biosynthesis. Homodimer (PubMed:22516296, PubMed:21233389). Interacts with ALOX5AP and LTC4S (PubMed:19233132). Interacts with COTL1, the interaction is required for stability and efficient catalytic activity (PubMed:19807693). Interacts with PIK3R1; this interaction bridges ALOX5 with CD40 after CD40 ligation in B cells and leads to the production of reactive oxygen species (ROS) (PubMed:21200133). Interacts (via PLAT domain) with DICER1 (via Dicer dsRNA-binding fold domain); this interaction enhances arachidonate 5-lipoxygenase activity and modifies the miRNA precursor processing activity of DICER1 (PubMed:19022417). Shuttles between cytoplasm and nucleus (PubMed:19233132). Found exclusively in the nucleus, when phosphorylated on Ser-272 (PubMed:18978352). Calcium binding promotes translocation from the cytosol and the nuclear matrix to the nuclear envelope and membrane association (PubMed:19233132, PubMed:3118366, PubMed:8245774, PubMed:16275640). Additional isoforms seem to exist. Serine phosphorylation by MAPKAPK2 is stimulated by arachidonic acid (PubMed:11844797, PubMed:18978352). Phosphorylation on Ser-524 by PKA has an inhibitory effect (PubMed:15280375). Phosphorylation on Ser-272 prevents export from the nucleus (PubMed:11844797, PubMed:18978352). Phosphorylation at Ser-524 is stimulated by 8-bromo-3',5'-cyclic AMP or prostaglandin E2 (PubMed:26210919). Belongs to the lipoxygenase family.