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Pedro Silva, Associate professor at Universidade Fernando Pessoa and researcher at the Biomolecular Simulation Lab at UCIBIO in Faculty of  Medicine at the University of Porto, together with Qi Cheng (Hebei Agricultural University) has explored the reaction mechanism of a key, light-activated, enzyme in chlorophyll biosynthesis using quantum chemical methods. This exciting work, which has just been published in the scientific journal ACS CatalysisAn Alternative Proposal for the Reaction Mechanism of Light-Dependent Protochlorophyllide Oxidoreductaseshows that the currently accepted mechanism is unfeasible and that instead a previously unsuspected light-induced electron transfer takes place a key active site residue to the substrate. 


Only a few instances of light-activated enzymes are known, and their reaction mechanisms remain mostly shrouded in mystery. One of them, the light-dependent protochlorophyllide oxidoreductase (LPChOR), plays a key role in the production of chlorophyll in plants and cyanobacteria and in the development of functional chloroplasts upon exposure to light.  Up until now, light was thought to excite the substrate (protochlorophyllide) and prime it for reaction with the organic electron donor NADPH. However, the quantum chemical and continuum electrostatic computations described in this new publication show that this proposal is incompatible with the high reaction rates observed experimentally. Instead, a new reaction mechanism involving light-induced electron transfer from the enzyme to the substrate was shown to be compatible with the experimental reaction rate. “This new mechanism involves radical chemistry in the active site, explains the effects of several mutations on the enzyme performance, and suggests novel interpretations for several intriguing experimental observations”, concludes Pedro Silva.



Original publication:

An Alternative Proposal for the Reaction Mechanism of Light-Dependent Protochlorophyllide Oxidoreductase
Pedro J. Silva and Qi Cheng
ACS Catal. 2022, 12, 4, 2589–2605