Fig. 3.

A: Schematic summarizing bisretinoid production in photoreceptor outer segments with processing in RPE. RAL, retinaldehyde. B. Structure of A2PE, A2-GPE, and A2E with UV-visible absorbance (nanometers). The structure includes an ether-linked (–O–) saturated alkyl chain at the sn-1 position; a vinyl ether (-O-C=C-) at the sn-1 position (plasmalogen) with alkyl groups; and an ester (–O–C=O–) linkage at the sn-1 position with alkyl groups. Positions on the GPE that are subject to hydrolysis by PLA₂ and PLD are indicated (pink arrows). Cleavage by PLA₂ yields lysoA2PE. Cleavage by PLD yields A2E. Carbon numbers on the glycerol backbone are indicated by 1, 2, and 3. Absorbance peaks at 440 and 340 nm can be assigned to the long and short arms of the molecule, respectively.