The photochemical reaction catalyzed by the enzyme protochlorophyllide oxidoreductase (POR), a rare example of a photoactivated enzyme, is a crucial step during chlorophyll biosynthesis and involves the fastest known biological hydride transfer. Structures of the enzyme with bound substrate protochlorophyllide (PChlide) and coenzyme NADPH have recently been published, opening up the possibility of using computational approaches to provide a comprehensive understanding of the excited state chemistry. Herein, we propose a complete mechanism for the photochemistry between PChlide and NADPH based on DFT and TDDFT calculations that is consistent with recent experimental data. In this multi-step mechanism, photoexcitation of the PChlide leads to electron transfer from NADPH to PChlide, which in turn facilitates hydrogen atom transfer by weakening the breaking C-H bond. This work rationalizes how photoexcitation facilitates hydride transfer in POR, and has more general implications for biological hydride transfer reactions.
|Publication status||Accepted/In press - 8 Mar 2022|
Research Beacons, Institutes and Platforms
- Manchester Institute of Biotechnology