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BACTERIORHODOPSIN FROM HALOBACTERIUM SALINARIUM IS A KEY COMPOUND IN BIOENERGETICS

Gabi Drochioiu

Abstract

Bacteriorhodopsin (bR) is a red-colored protein found in cell membranes of the organism Halobacterium salinarum, being considered as a light activated proton pump that transports protons across the plasma membrane. Because bacteriorhodopsin is one of the simplest ATP-producing systems known in biology, it has been the subject of intensive investigations. The bR photo-intermediates were seen in the mechanistic model considering that this protein links light energy to the translocation of protons across the bacterial membrane. However, once released outside the Halobacterium cell, the protons should return alone through the bacterial membrane via ATP synthase to produce ATP. Therefore, we reassess the electron crystallographic data used in parallel with X-ray measurements to study the post-illumination conformational changes of bR. Bacteriorhodopsin photointermediates have been defined in kinetic and spectroscopic terms as BR570, K590, L550, M412, N560, and O640. We recalculated the Forster cycle for bR and admitted that an energy quantum corresponding to the near infrared radiation could explain ATP formation and provide the most feasible molecular mechanism. Our hypothesis shows that the vectorial proton pumping mechanism is not fully correct. Protons are released due to bR excitation only as a secondary process and spread both inside and outside bacterial cells. Hence, protons cannot play an essential role in ATP production. Instead, spectral shift of 138 nm simultaneously with proton release corresponds to an energy quantum of 17.44 kcal/mol. Obviously, this energy can be used by ATP synthase to release one mole of ATP. We also revaluated different experimental data in the light of Eugen Macovschi's biostructural theory. Peter Mitchell?s hypothesis and the mechanism of action of uncoupling agents are also discussed here. Our hypothesis is consistent with experimental data and recent theories of other researchers, such as that of Paul Boyer.

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DOI resolver: doi.org/10.5593/sgem2019/6.1/s25.074

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