Proteorhodopsin's a photoactive retinylidene protein in marine bacterioplanktons. Just like the homologous pigment bacteriorhodopsin found in some archaea, it consists of a transmembrane protein bound to a retinal molecule and functions as a light-driven proton pump. Some members of the family (of more than 800 types) are believed to have sensory functions. Members are known to have different absorption spectra. Proteorhodopsin was first discovered in 2000. It was found in the genomes of several… (More on Proteorhodopsin)