bacteriorodopsina is photosynthetic Pigment used by Archaea, mainly Halobacteria . It acts as Pump of protons, that is to say, captures energy of the light cellular Membrane uses and it to move protons through . The proton gradient that is turns later into chemical energy.

The bacteriorodopsina is one integral membrane Protein found in bidimensional crystalline patches of color purple generally, that can occupy almost until 50% of the superficial area of the cell of the archaea. The elementary cell of the hexagonal lattice is made up of three identical protein chains, each rotated 120 degrees with respect to the other. Each seven chain this composed of helices transmembrana alpha and one deeply located retinal molecule in its interior, the typical structure of retinal proteins.

The conformation of the retinal molecule changes when absorbing a photon, producing a conformacional change in the surrounding protein and the pumping of the proton.

The color of the bacteriorodopsina molecule is the purple, most efficient for the green light absorption (wavelength of 500-650 nm, with the maximum of absorption in 568 nm).

three-dimensional tertiary structure of the bacteriorodopsina resembles the one of Rodopsina, the pigment that detects the light in Retina of the vertebrates. The rodopsinas also contain a retinal molecule, however, the functions of the rodopsina and the bacteriorodopsina are different and there is no homology in its sequences of amino acids. The rodopsina and the bacteriorodopsina belong to the receiving protein family 7TM, but the rodopsina is a connected receiver to proteins G and the bacteriorodopsina is not it. The structure of the bacteriorodopsina was solved in 1990, in the first use of electron Crystallography for the obtaining of proteinic structures at atomic level. Since then it has been used as it soles to construct models of the other connected receivers to proteins G before the cristalográficas structures were also available for those proteins.

Many homologous molecules are to the bacteriorodopsina. These include to Halorodopsina, chloride pump lead by the light (whose crystalline structure also is known). Also some channels activated directly by the light are included, such as Canalrodopsina .

The rest of the photosynthetic systems in bacteria, seaweed and plants use Chlorophyll or Bacterioclorofila, instead of bacteriorodopsina . These also produce a proton gradient, but of a way different and completely more indirect than implies one Chain of electron transport that uses several other proteins. In addition, other known pigments as antennas help chlorophylls to capture energy of the light, which are not present in the systems based on bacteriorodopsina. Finally, the photosynthesis based on chlorophyll is reconciled with the fixation of carbon (the incorporation of dioxide of carbon to organic molecules), which is not truth for the systems based on bacteriorodopsina. So it is probable that the photosynthesis was developed independently at least twice, one in bacteria and another one in archaea.