...Here we report a previously unidentified fluorescent bisretinoid by UPLC coupled to photodiode array detection, fluorescence, and electrospray ionization mass spectrometry (UPLC-PDA-FLR-ESI-MS) (Kim HJ, Sparrow JR, J Lipid Res 59:1620-1629, 2018). This novel bisretinoid is 1-octadecyl-2-lyso-sn-glycero A2PE (alkyl ether lysoA2PE). The structural assignment was based on molecular weight (m/z 998), UV-visible absorbance maxima (340, 440 nm), and retention time (73 minutes) and was corroborated by biomimetic synthesis using all-trans-retinal and glycerophosphoethanolamine analogues as starting materials. In mechanistic studies, A2PE was hydrolyzed by PLA2, and plasmalogen lysoA2PE was cleaved under acidic conditions. Unprecedented UPLC detection of the bisretinoid alkyl ether lysoA2PE in human RPE but not in neural retina indicates that the phospholipase A2 activity that generates the latter bisretinoid resides in RPE.