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. 2022 Jul 18;9:914457. doi: 10.3389/fnut.2022.914457

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Copyright © 2022 Thirunavukarasu, Ross and Gilbert.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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The “flipping” function of ABCA4. 11-cis retinal accumulates in darker conditions as opsins are saturated, whereas all-trans retinal is produced by photoisomerisation in lighter conditions. Retinal associates with membranal phosphatidylethanolamine (PE) to form N-cis-retinylidene-PE (NcRPE) and N-trans-retinylidene-PE (NtRPE), which ABCA4 flips across the membrane at the cost of ATP hydrolysis. NcRPE and NtRPE dissociate, and 11-cis retinal undergoes chemical isomerisation, allowing all-trans retinal to reenter the visual cycle.