Rhodopsins are light-sensitive molecules composed of a protein (opsin) and retinal (derivative of vitamin a). opsin is a membrane protein with several alpha-helical segments that loop back and forth through the plasma membrane. there are two classes of rhodopsins. according to oded beje, one class has relatively slow dynamics (a photocycle of approximately 0.5 second) and is well suited for light detection. the second class has faster dynamics (a photocycle of approximately 0.02 seconds) and is well suited for chemiosmosis-pumping of protons or chloride ions across cell membranes. oded beje was the first, in september 2000, to report on a rhodopsin (proteorhodopsin) found in the domain bacteria. [source: o. beje et al., science 289 (2000): 1902.] proteorhodopsin consists of a single polypeptide chain. what is the highest level of structure found in this protein?