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. 2004 Jul 26;101(32):11668–11672. doi: 10.1073/pnas.0403499101

Fig. 1.

Fig. 1.

Lipofuscin fluorophores as by-products of the visual cycle. (A) The retinoid cycle and formation of the lipofuscin fluorophores A2E, iso-A2E, and all-trans-retinal (ATR) dimer. Upon the photoisomerization of 11-cis-retinal, all-trans-retinal is released from rhodopsin and reduced to all-trans-retinol by all-trans-retinol dehydrogenase (atrDH). Lecithin retinol acyltransferase (LRAT) generates all-trans-retinyl esters from all-trans-retinol, and RPE65 presents retinyl esters to isomerohydrolase (IMH) for processing to 11-cis-retinol. 11-cis-retinol is then oxidized by 11-cis-retinol dehydrogenase (11-cRDH) to regenerate 11-cis-retinal. All-trans-retinal that evades reduction reacts with phosphatidylethanolamine (PE) (2:1) to generate the precursor A2-PE, from which A2E and iso-A2E form, or ATR dimer. (B) Structures of A2E and iso-A2E. These pigments interconvert under the influence of light.