porphyropsin

Porphyropsin is a purple pigment found in the retinal rods of freshwater fish. It is similar to rhodopsin but uses a different chromophore, 3-dehydroretinal, instead of retinal. This difference shifts the spectral sensitivity of porphyropsins toward the red end of the spectrum compared to retinal-based pigments with the same opsin. Photoreceptors, like those containing porphyropsin, are cells in the retina that detect light. They contain photopigments, which are composed of a protein called opsin and a chromophore that absorbs light photons.12