The function of CYP4F3 (cytochrome P450 family 4 subfamily F member 3, ENSG00000186529) is as follows. A cytochrome P450 monooxygenase involved in the metabolism of various endogenous substrates, including fatty acids and their oxygenated derivatives (oxylipins) (PubMed:11461919, PubMed:15145985, PubMed:16547005, PubMed:16820285, PubMed:18065749, PubMed:18182499, PubMed:18577768, PubMed:8486631, PubMed:9675028). Mechanistically, uses molecular oxygen inserting one oxygen atom into a substrate, and reducing the second into a water molecule, with two electrons provided by NADPH via cytochrome P450 reductase (CPR; NADPH-ferrihemoprotein reductase) (PubMed:9675028). May play a role in inactivation of pro- inflammatory and anti-inflammatory oxylipins during the resolution of inflammation (PubMed:11461919, PubMed:15145985, PubMed:15364545, PubMed:16547005, PubMed:16820285, PubMed:18065749, PubMed:18182499, PubMed:18577768, PubMed:8486631, PubMed:9675028). {ECO:0000269|PubMed:11461919, ECO:0000269|PubMed:15145985, ECO:0000269|PubMed:15364545, ECO:0000269|PubMed:16547005, ECO:0000269|PubMed:16820285, ECO:0000269|PubMed:18065749, ECO:0000269|PubMed:18182499, ECO:0000269|PubMed:18577768, ECO:0000269|PubMed:8486631, ECO:0000269|PubMed:9675028}. [Isoform CYP4F3A]: Catalyzes predominantly the oxidation of the terminal carbon (omega-oxidation) of oxylipins in myeloid cells, displaying higher affinity for arachidonate metabolite leukotriene B4 (LTB4) (PubMed:11461919, PubMed:15364545, PubMed:8486631, PubMed:9675028). Inactivates LTB4 via three successive oxidative transformations to 20-hydroxy-LTB4, then to 20-oxo-LTB4 and to 20- carboxy-LTB4 (PubMed:9675028). Has omega-hydroxylase activity toward long-chain fatty acid epoxides with preference for 8,9-epoxy- (5Z,11Z,14Z)-eicosatrienoate (EET) and 9,10-epoxyoctadecanoate (PubMed:15145985). Omega-hydroxylates monohydroxy polyunsaturated fatty acids (PUFAs), including hydroxyeicosatetraenoates (HETEs) and hydroxyeicosapentaenoates (HEPEs), to dihydroxy compounds (PubMed:15364545, PubMed:9675028). Contributes to the degradation of saturated very long-chain fatty acids (VLCFAs) such as docosanoic acid, by catalyzing successive omega-oxidations to the corresponding dicarboxylic acid, thereby initiating chain shortening (PubMed:18182499). Has low hydroxylase activity toward PUFAs (PubMed:11461919, PubMed:18577768). {ECO:0000269|PubMed:11461919, ECO:0000269|PubMed:15145985, ECO:0000269|PubMed:15364545, ECO:0000269|PubMed:18182499, ECO:0000269|PubMed:18577768, ECO:0000269|PubMed:8486631, ECO:0000269|PubMed:9675028}. [Isoform CYP4F3B]: Catalyzes predominantly the oxidation of the terminal carbon (omega-oxidation) of polyunsaturated fatty acids (PUFAs) (PubMed:11461919, PubMed:16820285, PubMed:18577768). Participates in the conversion of arachidonic acid to 20- hydroxyeicosatetraenoic acid (20-HETE), a signaling molecule acting both as vasoconstrictive and natriuretic with overall effect on arterial blood pressure (PubMed:11461919, PubMed:16820285, PubMed:18577768). Has high omega-hydroxylase activity toward other PUFAs, including eicosatrienoic acid (ETA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) (PubMed:16820285, PubMed:18577768). Can also catalyze the oxidation of the penultimate carbon (omega-1 oxidation) of PUFAs with lower efficiency (PubMed:18577768). Contributes to the degradation of saturated very long-chain fatty acids (VLCFAs) such as docosanoic acid and hexacosanoic acid, by catalyzing successive omega-oxidations to the corresponding dicarboxylic acids, thereby initiating chain shortening (PubMed:16547005, PubMed:18182499). Omega-hydroxylates long-chain 3-hydroxy fatty acids, likely initiating the oxidative conversion to the corresponding 3-hydroxydicarboxylic fatty acids (PubMed:18065749). Has omega-hydroxylase activity toward long-chain fatty acid epoxides with preference for 8,9-epoxy- (5Z,11Z,14Z)-eicosatrienoate (EET) and 9,10-epoxyoctadecanoate (PubMed:15145985). {ECO:0000269|PubMed:11461919, ECO:0000269|PubMed:15145985, ECO:0000269|PubMed:16547005, ECO:0000269|PubMed:16820285, ECO:0000269|PubMed:18065749, ECO:0000269|PubMed:18182499, ECO:0000269|PubMed:18577768}.