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). The cholesterol ester is then transported back to the liver. Has a preference for plasma 16:0-18:2 or 18:O-18:2 phosphatidylcholines. 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. Together with APOE and the cholesterol transporter ABCA1, plays a key role in the maturation of glial-derived, nascent lipoproteins. Required for remodeling high-density lipoprotein particles into their spherical forms (By similarity). a 1,2-diacyl-sn-glycero-3-phosphocholine + a sterol = a 1-acyl-sn-glycero-3-phosphocholine + a sterol ester APOA1 is the most potent activator in plasma. Also activated by APOE, APOC1 and APOA4 (By similarity). Secreted into blood plasma. Produced in astrocytes and secreted into cerebral spinal fluid (CSF) (By similarity). Most abundant in liver and cerebellum. Belongs to the AB hydrolase superfamily. Lipase family.