Central enzyme in the extracellular metabolism of plasma lipoproteins. Synthesized mainly in the liver and secreted into plasma where it converts cholesterol and phosphatidylcholines (lecithins) to cholesteryl esters and lysophosphatidylcholines on the surface of high and low density lipoproteins (HDLs and LDLs) (PubMed:19065001). The cholesterol ester is then transported back to the liver. Also produced in the brain by primary astrocytes, and esterifies free cholesterol on nascent APOE-containing lipoproteins secreted from glia and influences cerebral spinal fluid (CSF) APOE- and APOA1 levels (PubMed:19065001). Together with APOE and the cholesterol transporter ABCA1, plays a key role in the maturation of glial-derived, nascent lipoproteins (PubMed:19065001). Required for remodeling high-density lipoprotein particles into their spherical forms (PubMed:19065001). Has a preference for plasma 16:0-18:2 or 18:O-18:2 phosphatidylcholines (PubMed:8820107). Catalyzes the hydrolysis of 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine (platelet-activating factor or PAF) to 1-O-alkyl-sn-glycero-3-phosphocholine (lyso-PAF) (PubMed:10393212). Also catalyzes the transfer of the acetate group from PAF to 1-hexadecanoyl-sn-glycero-3-phosphocholine forming lyso-PAF (By similarity). Catalyzes the esterification of (24S)-hydroxycholesterol (24(S)OH-C), also known as cerebrosterol to produce 24(S)OH-C monoesters (By similarity). a 1,2-diacyl-sn-glycero-3-phosphocholine + a sterol = a 1-acyl-sn-glycero-3-phosphocholine + a sterol ester a 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine + H2O = 1-O-alkyl-sn-glycero-3-phosphocholine + acetate + H(+) (24S)-hydroxycholesterol + 1-hexadecanoyl-2-acyl-sn-glycero-3-phosphocholine = (24S)-24-hydroxycholesterol ester + 1-hexadecanoyl-sn-glycero-3-phosphocholine (24S)-hydroxycholesterol + 1-hexadecanoyl-2-(9Z,12Z-octadecadienoyl)-sn-glycero-3-phosphocholine = (24S)-hydroxycholesterol 3-linoleoate + 1-hexadecanoyl-sn-glycero-3-phosphocholine 1-hexadecanoyl-2-(5Z,8Z,11Z,14Z-eicosatetraenoyl)-sn-glycero-3-phosphocholine + cholesterol = 1-hexadecanoyl-sn-glycero-3-phosphocholine + cholesteryl (5Z,8Z,11Z,14Z)-eicosatetraenoate 1-hexadecanoyl-2-(9Z-octadecenoyl)-sn-glycero-3-phosphocholine + cholesterol = 1-hexadecanoyl-sn-glycero-3-phosphocholine + cholesteryl (9Z-octadecenoate) 1-hexadecanoyl-2-(8Z,11Z,14Z-eicosatrienoyl)-sn-glycero-3-phosphocholine + cholesterol = 1-hexadecanoyl-sn-glycero-3-phosphocholine + cholesteryl (8Z,11Z,14Z)-eicosatrienoate 1-hexadecanoyl-2-(5Z,8Z,11Z-eicosatrienoyl)-sn-glycero-3-phosphocholine + cholesterol = 1-hexadecanoyl-sn-glycero-3-phosphocholine + cholesteryl (5Z,8Z,11Z)-eicosatrienoate 1-hexadecanoyl-2-(5Z,8Z,11Z,14Z,17Z-eicosapentaenoyl)-sn-glycero-3-phosphocholine + cholesterol = (5Z,8Z,11Z,14Z,17Z-eicosapentaenoyl)-cholesterol + 1-hexadecanoyl-sn-glycero-3-phosphocholine 1-hexadecanoyl-2-(9Z,12Z-octadecadienoyl)-sn-glycero-3-phosphocholine + cholesterol = 1-hexadecanoyl-sn-glycero-3-phosphocholine + cholesteryl (9Z,12Z)-octadecadienoate 1-hexadecanoyl-2-(6Z,9Z,12Z-octadecatrienoyl)-sn-glycero-3-phosphocholine + cholesterol = (6Z,9Z,12Z-octadecatrienoyl)-cholesterol + 1-hexadecanoyl-sn-glycero-3-phosphocholine 1-hexadecanoyl-2-(11Z,14Z,17Z-eicosatrienoyl)-sn-glycero-3-phosphocholine + cholesterol = (11Z,14Z,17Z-eicosatrienoyl)-cholesterol + 1-hexadecanoyl-sn-glycero-3-phosphocholine 1-hexadecanoyl-2-(9Z,12Z,15Z-octadecatrienoyl)-sn-glycero-3-phosphocholine + cholesterol = (9Z,12Z,15Z-octadecatrienoyl)-cholesterol + 1-hexadecanoyl-sn-glycero-3-phosphocholine 1-hexadecanoyl-2-(9Z,12Z-octadecadienoyl)-sn-glycero-3-phosphocholine + H2O = (9Z,12Z)-octadecadienoate + 1-hexadecanoyl-sn-glycero-3-phosphocholine + H(+) 1-hexadecanoyl-2-(5Z,8Z,11Z,14Z-eicosatetraenoyl)-sn-glycero-3-phosphocholine + H2O = (5Z,8Z,11Z,14Z)-eicosatetraenoate + 1-hexadecanoyl-sn-glycero-3-phosphocholine + H(+) 1-hexadecanoyl-sn-glycero-3-phosphocholine + a 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine = 1-hexadecanoyl-2-acetyl-sn-glycero-3-phosphocholine + 1-O-alkyl-sn-glycero-3-phosphocholine APOA1 is the most potent activator in plasma. Also activated by APOE, APOC1 and APOA4. Secreted into blood plasma (PubMed:8820107). Produced in astrocytes and secreted into cerebral spinal fluid (CSF) (By similarity). Detected in blood plasma (PubMed:8820107). Produced and secreted by astrocytes (at protein level) (PubMed:19065001). Abundantly expressed in liver, brain and testis with highest levels in liver. In the brain, found in cerebellum, cerebral cortex, hippocampus and brain stem. Located to neurons and neuroglia. In the testis, expressed days 4,8, 14, and 35 of postnatal life with highest levels at day 35. In the brain, expressed in fetal stages and levels begin to rise after day 4 after birth and continue to increase through suckling and weaning reaching a peak at postnatal day 24. In the liver, expressed in fetal life from day 16-21 of gestation with a 3-fold increase in the four final days of gestation. Null mice exhibit a 7-fold increase in the cholesteryl ester fatty acid CEFA ratio of APOB lipoprotein CEs. There is also a 3.6 increase in vascular ring O(2) production and plasma phospholipid (PL)-bound-F2-isoprostane levels. This effect is paradoxically reversed in the APOE knockout background (PubMed:11809774, PubMed:11893779). Mice show a significant reduction in total cholesterol, HDL-cholesterol, apoA-I, serum paraoxonase and PAF acetylhydrolase enzyme activities and show a modest (36%) but significant increase in apoJ levels (PubMed:10393212). Belongs to the AB hydrolase superfamily. Lipase family.