The extracellular domain appears to act as a ‘plug’ that may prevent the retinal from protruding from the protein upon isomerization, thereby forcing the protein to adapt to the all-trans ...
Biochemical Measurements of Free Opsin in Macular Degeneration Eyes: Examining the 11-CIS Retinal Deficiency Hypothesis of Delayed Dark Adaptation (An American Ophthalmological Society Thesis).