Porphyrins as photosensitizers to enhance night vision

The primary event in mammalian vision is a light-initiated cis-to-trans isomerization of the retinal chromophore bound, via a protonated Schiff base, to a lysine residue in the opsin apoprotein (Figure 1A).1 This isomerization activates the protein which triggers a series of events resulting in a signal to the brain. This has been a basic tenet of our understanding of vision. Rod-rhodopsin, the opsin-retinal complex responsible for night vision, is a G-protein-coupled receptor, activated by light with an absorbance maximum at 500 nm. As the absorption from rhodopsin is minute above 600 nm, the pigment is not believed to be involved in vision at longer wavelengths. It has been proposed that the visual signal transduction pathway in a species of deep-sea fish involves the use of photosensitizers.2 Molecules derived from chlorophyll 650 are thought to absorb longer-wavelength light and transfer the gained energy to shorter