Abiogenic Photophosphorylation of ADP to ATP Sensitized by Flavoproteinoid Microspheres

Abstract

A model for abiogenic photophosphorylation of ADP by orthophosphate to yield ATP was studied. The model is based on the photochemical activity of flavoproteinoid microspheres that are formed by aggregation in an aqueous medium of products of thermal condensation of a glutamic acid, glycine and lysine mixture (8:3:1) and contain, along with amino acid polymers (proteinoids), abiogenic isoalloxazine (flavin) pigments. Irradiation of aqueous suspensions of microspheres with blue visible light or ultraviolet in the presence of ADP and orthophosphate resulted in ATP formation. The yield of ATP in aerated suspensions was 10-20% per one mol of starting ADP. Deaeration reduced the photophosphorylating activity of microspheres five to 10 times. Treatment of aerated microsphere suspensions with superoxide dismutase during irradiation partially suppressed ATP formation. Deaerated microspheres restored completely their photophosphorylating activity after addition of hydrogen peroxide to the suspension. The photophosphorylating activity of deaerated suspensions of flavoproteinoid microspheres was also recovered by introduction of Fe3+-cytochrome c, an electron acceptor alternative to oxygen. On the basis of the results obtained, a chemical mechanism of phosphorylation is proposed in which the free radical form of reduced flavin sensitizer (F1H*) and ADP are involved.

Peptide‐dominated membranes preceding the genetic takeover by RNA: latest thinking on a classic controversy

“…(68) A potential solution could be some primitive coupling of pyrophosphate bond formation with light-harvesting pigments and polarized electron/proton mobilization, as modeled by light-dependent formation of ATP at glycine-rich flavoproteinoid microspheres. (69,70) Ribonucleoside triphosphates are relatively derived metabolites; so ATP has probably not been the primary energy currency of protometabolism to begin with. Other candidates for such a role are more primitive energy-rich compounds, such as glycerol phosphates, phosphoribosyl pyrophosphate (PRPP) or isopentenyl pyrophosphate (IPP).…”

“…In the recurrence of ebb and flow, the Darwinian principle -the fittest entities surviving from one perturbation cycle to the next -became effective long before the emergence of a genuine cell division cycle. With some form of photosynthesis in place, (73,74) perhaps powered by precursors of a light-driven proton pump, (75) simple sugar moieties became available, and their polymerization to oligosaccharides could significantly contribute to overall stickiness in the biogenic surface agglomerates. The gelling properties of polysaccharides could modulate water activity under drying conditions on sun-torched mud flats.…”

Why Flavins Are not Competitors of Chlorophyll in the Evolution of Biological Converters of Solar Energy

“…The E o ′ value for EDTA is equal to +0.40 V) [31]. In the presence of EDTA, excited coenzyme flavin molecules and abiogenic isoalloxazine pigments transit to the reduced state, or (in the presence of an electron acceptor, for instance, Fe 3+ -cytochrome c ) they photocatalyze the reduction of this acceptor [32,33]. …”

“…The organic components of the photophosphorylating system, polyamino acid matrix (the template) and flavin chromophore are the products of the thermolysis of anhydrous mixtures of amino acids (glutamic acid, lysine and glycine) in an anoxygenic medium [7–9]. When this product contacts water in the presence of orthosilicic acid, it self-aggregates to form the so-called “Fox’s proteinoid microspheres” [10,33]. Irradiation of this microsphere suspension with blue or UV-A/B light causes the phosphorylation of ADP by orthophosphate to form ATP.…”

“…The photophosphorylation process was sensitive to superoxide dismutase, and activity depended on the presence of agents that could ensure the oxidative regeneration of flavin, including dioxygen, hydrogen peroxide, or “non-oxygenic” electron acceptors (e.g., Fe 3+ -cytochrome c ( E o ′ = +0.25 V)) [33]. Thus, photophosphorylation is related to light-induced electron transfer and likely involves the formation of a flavin-free radical.…”