Abstract
Excited flavin molecules can photocatalyze reactions, leading to the accumulation of free energy in the products, and the data accumulated through biochemical experiments and by modeling prebiological processes suggest that flavins were available in the earliest stages of evolution. Furthermore, model experiments have shown that abiogenic flavin conjugated with a polyamino acid matrix, a pigment that photocatalyzes the phosphorylation of ADP to form ATP, could have been present in the prebiotic environment. Indeed, excited flavin molecules play key roles in many photoenzymes and regulatory photoreceptors, and the substantial structural differences between photoreceptor families indicate that evolution has repeatedly used flavins as chromophores for photoreceptor proteins. Some of these photoreceptors are equipped with a light-harvesting antenna, which transfers excitation energy to chemically reactive flavins in the reaction center. The sum of the available data suggests that evolution could have led to the formation of a flavin-based biological converter to convert light energy into energy in the form of ATP.
Highlights
Since the Precambrian Era, the conversion of energy from solar light in the biosphere has been performed almost exclusively through chlorophyll-based photosynthesis [1], and there are reasons to believe that “...photosynthesis began early in Earth’s history but was probably not one of the earliest metabolisms, and ... the earliest forms of photosynthesis were anoxygenic, with oxygenic forms arising significantly later” [2]
When compared to photosynthesis, this mechanism is a truncated version of a light energy converter: Intermolecular electron transfer does not mediate the formation of the proton gradient that occurs after the excitation of bacteriorhodopsin
Because flavins were repeatedly recruited to perform photoreceptor functions, we suggest that one such attempt could lead to the formation of a flavin-based converter of light energy
Summary
Since the Precambrian Era, the conversion of energy from solar light in the biosphere has been performed almost exclusively through chlorophyll-based photosynthesis [1], and there are reasons to believe that “...photosynthesis began early in Earth’s history but was probably not one of the earliest metabolisms, and ... the earliest forms of photosynthesis were anoxygenic, with oxygenic forms arising significantly later” [2]. Under certain conditions, ATP may be the only product from the photosynthetic conversion of light energy This is the case during cyclic photophosphorylation in plant chloroplasts in which electron flow begins in PS1, is transferred via ETC and returns to the PS1 chlorophyll. One example is a mechanism discovered in cells of the halophilic archaeon Halobacterium salinarum (H. halobium) This mechanism is based on the activity of bacteriorhodopsin, a retinal-binding protein that is an integral protein in the membrane of this organism and absorbs green light with a maximum wavelength of 568 nm. When compared to photosynthesis, this mechanism is a truncated version of a light energy converter: Intermolecular electron transfer does not mediate the formation of the proton gradient that occurs after the excitation of bacteriorhodopsin. It is remarkable that, during evolution, one of these families has acquired a light-harvesting mechanism that is similar to the antenna of the photosynthetic apparatus and increases the flow of photon energy to the reaction (photochemical) center
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