Efficiently catalyzes the conversion of all-trans retinol (also called vitamin A1, the precursor of 11-cis retinal) to 3,4-didehydroretinol (also called vitamin A2, the precursor of 11-cis 3,4-didehydroretinal). Also acts on all-trans retinal and all-trans retinoic acid. The replacement of 11-cis retinal chromophore in photopigments with 11-cis 3,4-didehydroretinal enhances sensitivity to long-wavelength light. This may improve vision in fresh water which is often turbid. all-trans-retinol + 2 H(+) + O2 + 2 reduced [adrenodoxin] = all-trans-3,4-didehydroretinol + 2 H2O + 2 oxidized [adrenodoxin] Following L-thyroxine, expressed in the retinal pigment epithelium (at protein level). In the retinal pigment epithelium, up-regulated by L-thyroxine (at protein level). Mutant fish survive to adulthood without overt developmental abnormalities. Upon treatment with L-thyroxine, the mutant fish eyes fail to produce any vitamin A2 and their photoreceptors fail to undergo a red-shift in sensitivity. Belongs to the cytochrome P450 family. Truncated N-terminus. Truncated N-terminus. Truncated N-terminus. Seeing through the murk - Issue 192 of June 2017