Hydrolyzes the ester bond of the acyl group attached at the sn-1 position of phosphatidylserines (phospholipase A1 activity) and 1-acyl-2-lysophosphatidylserines (lysophospholipase activity) in the pathway of phosphatidylserines acyl chain remodeling (PubMed:10196188). Cleaves phosphatidylserines exposed on the outer leaflet of the plasma membrane of apoptotic cells producing 2-acyl-1-lysophosphatidylserines, which in turn enhance mast cell activation and histamine production (By similarity). Has no activity toward other glycerophospholipids including phosphatidylcholines, phosphatidylethanolamines, phosphatidic acids or phosphatidylinositols, or glycerolipids such as triolein (By similarity). Hydrolyzes lyso-PS but not PS. a 1,2-diacyl-sn-glycero-3-phospho-L-serine + H2O = a 2-acyl-sn-glycero-3-phospho-L-serine + a fatty acid + H(+) 1,2-di-(9Z)-octadecenoyl-sn-glycero-3-phospho-L-serine + H2O = (9Z)-octadecenoate + 2-(9Z-octadecenoyl)-sn-glycero-3-phospho-L-serine + H(+) 1-hexadecanoyl-2-(5Z,8Z,11Z,14Z-eicosatetraenoyl)-sn-glycero-3-phospho-L-serine + H2O = 2-(5Z,8Z,11Z,14Z)-eicosatetraenoyl-sn-glycero-3-phospho-L-serine + H(+) + hexadecanoate a 1-acyl-sn-glycero-3-phospho-L-serine + H2O = a fatty acid + H(+) + sn-glycero-3-phospho-L-serine 1-(9Z-octadecenoyl)-sn-glycero-3-phospho-L-serine + H2O = (9Z)-octadecenoate + H(+) + sn-glycero-3-phospho-L-serine 1-(9Z-octadecenoyl)-sn-glycero-3-phospho-L-serine + H2O = (9Z)-octadecenoate + H(+) + sn-glycero-3-phospho-L-serine Widely expressed. Expressed in placenta, prostate and liver. Weakly or not expressed in skin, leukocytes, platelets, colon, spleen, lung, muscle and kidney. Belongs to the AB hydrolase superfamily. Lipase family.