Retinal-specific phospholipid-transporting ATPase ABCA4

Flippase that catalyzes in an ATP-dependent manner the transport of retinal-phosphatidylethanolamine conjugates like the 11-cis and all-trans isomers of N-retinylidene-phosphatidylethanolamine from the lumen to the cytoplasmic leaflet of photoreceptor outer segment disk membranes, where N-cis-retinylidene-phosphatidylethanolamine (N-cis-R-PE) is then isomerized to its all-trans isomer (N-trans-R-PE) and reduced by RDH8 to produce all-trans-retinol (all-trans-rol) and therefore prevents the accumulation of excess of 11-cis-retinal and its schiff-base conjugate and the formation of toxic bisretinoid. May display both ATPase and GTPase activity that is strongly influenced by the lipid environment and the presence of retinoid compounds. Binds the unprotonated form of N-retinylidene-phosphatidylethanolamine with high affinity in the absence of ATP, and ATP binding and hydrolysis induce a protein conformational change that causes the dissociation of N-retinylidene-phosphatidylethanolamine (By similarity).