BACTERIORHODOPSIN - THE SIMPLEST BIOENERGETIC SYSTEM FOR ATP PRODUCTION

Abstract

Bacteriorhodopsin (BRh), which is present in the cell membranes of the archaeon Halobacterium salinarum, harvests light wave energy which causes conformational changes in this retinal protein leading to the release of adenosine triphosphate (ATP) by ATP synthase. Since some protons are released during light-induced excitation of BRh molecules, the chemiosmotic hypothesis advanced by Peter Mitchell was used to explain the ATP formation by translocation of protons across the simple membranes of H. salinarum. However, protons can be released as a result of photoexcitation of some molecules, and these protons are only responsible for increasing the acidity (pKa) of their solutions; therefore, the protons released by BRh probably have no role in ATP production. In contrast, the 138 nm spectral shift between the two photointermediates, L550 and M412, corresponds to an energy amount of 17.41 kcal/mole, which can be successfully absorbed by ATP synthase as near-infrared radiation (NIR). The conformational changes of F0 ATP-synthase can induce the rotation of F1 ATP-synthase, which is associated with the removal of ATP molecules already formed by F1 ATP-synthase from ADP and inorganic phosphate. The NIR radiant energy can thus be confusingly associated with proton release and not with direct light-induced ATP formation. The already proposed mechanism of ATP production by BRh-ATP-synthase system is supported by a large body of literature data. However, such data that contradict old theories can be interpreted in the light of new understandings of living organisms. Therefore, a new perspective on ATP production in biological systems from the simplest to higher organisms is required.