Characterization of Exogenous Mediators for Electron Extraction from in Vitro photosynthesis

In vitro photosynthesis has garnered attention over the past decade as a novel system for generating an electrical current in a bio-solar cell. Our lab is focused on harnessing the reducing power of photosynthesis to catalyze in vitro enzymatic reactions, which requires a solid understanding of photosynthetic functions. Past characterizations of in vitro photosynthetic electron transport have relied on fluorescence measurements of chlorophyll pigments or electrical output of photosynthetic components [1,2]. Herein we describe a novel method for detecting reduction of exogenous mediators through ROS detection with the chemical luminol. Multiple quinones, whose structure and reduction potential vary, were used to characterize electron extraction from a photosynthetically active algal extract. The composition of the reaction buffer and the source of light were routinely adjusted to elucidate conditions that maximized electron harvesting. It was found that calcium greatly increased the reduction of the low redox potential mediator Anthraquinone 2-sulfonate (AQS), with other additives having varying effects on the different quinones tested. The light cycle used to stimulate in vitro photosynthesis and exposure to Triton X-100 also had profound effects on the reduction of exogenous quinones. Our findings can be utilized for tuning the environment of In vitro photosynthesis for the specific objective of a researcher, advancing the potential of bio-solar cells and in vitro enzymatic reactions as viable alternatives for energy.

1. Longatte, G., Rappaport, F., Wollman, F.-A., Guille-Collignon, M. & Lemaître, F. Mechanism and analyses for extracting photosynthetic electrons using exogenous quinones – what makes a good extraction pathway? Photochemical & Photobiological Sciences 15, 969–979 (2016).

2. Hasan, K. et al. Photobioelectrocatalysis of Intact Chloroplasts for Solar Energy Conversion. ACS Catal. 7, 2257–2265 (2017).