Evaluation of photosynthetic electrons derivation by exogenous redox mediators

Abstract

Oxygenic photosynthesis is the complex process that occurs in plants or algae by which the energy from the sun is converted into an electrochemical potential that drives the assimilation of carbon dioxide and the synthesis of carbohydrates. Quinones belong to a family of species commonly found in key processes of the Living, like photosynthesis or respiration, in which they act as electron transporters. This makes this class of molecules a popular candidate for biofuel cell and bioenergy applications insofar as they can be used as cargo to ship electrons to an electrode immersed in the cellular suspension. Nevertheless, such electron carriers are mostly selected empirically. This is why we report on a method involving fluorescence measurements to estimate the ability of seven different quinones to accept photosynthetic electrons downstream of photosystem II, the first protein complex in the light-dependent reactions of oxygenic photosynthesis. To this aim we use a mutant of Chlamydomonas reinhardtii, a unicellular green alga, impaired in electron downstream of photosystem II and assess the ability of quinones to restore electron flow by fluorescence. In this work, we defined and extracted a "derivation parameter" D that indicates the derivation efficiency of the exogenous quinones investigated. D then allows electing 2,6-dichlorobenzoquinone, 2,5-dichlorobenzoquinone and p-phenylbenzoquinone as good candidates. More particularly, our investigations suggested that other key parameters like the partition of quinones between different cellular compartments and their propensity to saturate these various compartments should also be taken into account in the process of selecting exogenous quinones for the purpose of deriving photoelectrons from intact algae.

Redesigning the QA binding site of Photosystem II allows reduction of exogenous quinones

“…The present fluorescence analysis shows that DMBQ is a far less efficient PSII electron acceptor than DCBQ. Its lower reactivity with the plastoquinone pool may be partly due to its relatively negative midpoint potential compared with that of the two other quinones we studied25, but it is also consistent with a lower partitioning in the thylakoid membranes as suggested by the remarkably low quenching capacity of DMBQ (Fig. 2b and ref.…”

“…Thus, DMBQ poorly interacts with the Q B binding site and the downstream plastoquinone pool with which Q B is at equilibrium. Since the three quinones are benzoquinones that do not differ greatly in terms of reduction potential of their relevant redox couples, all the three quinones can readily accept electrons based on the midpoint potential data25. We therefore interpret this poor interaction, as being due to the mediocre partitioning of DMBQ into the thylakoid membranes.…”

Electrocatalytic Mechanism Involving Michaelis–Menten Kinetics at the Preparative Scale: Theory and Applicability to Photocurrents from a Photosynthetic Algae Suspension With Quinones

“…[26,27] Then the photochemical rate (v max )h as been adapted from mathematican umerical simulations. An example is depictedi n Figure5.T he simulation shows an encouraginga greement between the experimental and predicted photocurrents.…”

“…[23][24][25] In this context,w er ecently benchmarked the ability of several exogenous quinones to harvestp hotosynthetic electrons from the green unicellular algae Chlamydomonas reinhardtii. [26] Furthermore, am odeling was established and evidenced that the extractionc orresponds to Michaelis-Menten-like kinetics. [27] Such results were used to extract photosynthetic electrons from an algae suspension at the preparative scale (with ac entimetre-sized carbon gauze as the collecting electrode) that faIn the past years, many strategies have been implemented to benefitfrom oxygenic photosynthesis to harvest photosynthetic electrons and produce as ignificant photocurrent.…”

“…)o ft he F = f(quinone concentration) curve established elsewhere) [26,27] and the photochemical rate named v max (in mol s À1 ;t hat is, the maximal quinone reduction rate with a100 %y ield). [29] If considering firstly the steady-state behaviour,t he chemical reaction and electrochemical reactionr ates are equal.…”