Retinal-specific phospholipid-transporting ATPase ABCA4 (ABCA4)

From the visual cycle, acts as an inward-directed retinoid flipase, retinoid substrates imported by ABCA4 in the extracellular or intradiscal (pole ) membrane surfaces to the cytoplasmic membrane surface are all-trans-retinaldehyde (ATR) and N-retinyl-phosphatidyl-ethanolamine (NR-PE). Once transported to the cytoplasmic surface, ATR is reduced to vitamin A by trans- retinol dehydrogenase (tRDH) and then moved to the retinal pigment epithelium (RPE) in which it is converted to 11-cis-retinal.

May play a role in photoresponse, removing ATR/NR-PE in the extracellular photoreceptor surfaces during bleach recovery. .