Simulating the low-temperature, metastable electrochromism of Photosystem I: Applications to Thermosynechococcus vulcanus and Chroococcidiopsis thermalis

Low-temperature, metastable electrochromism has been used as a tool to assign pigments in Photosystem I (PS I) from Thermosynechococcus vulcanus and both the white light and far-red light (FRL) forms of Chroococcidiopsis thermalis. We find that a minimum of seven pigments is required to satisfactorily model the electrochromism of PS I. Using our model, we provide a short list of candidates for the chlorophyll f pigment in FRL C. thermalis that absorbs at 756 nm, whose identity, to date, has proven to be controversial. Specifically, we propose the linker pigments A40 and B39 and two antenna pigments A26 and B24 as defined by crystal structure 1JB0. The pros and cons of these assignments are discussed, and we propose further experiments to better understand the functioning of FRL C. thermalis. Published under an exclusive license by AIP Publishing.

Automated summary

Low-temperature, metastable electrochromism has been used to identify pigments in Photosystem I (PS I) from Thermosynechococcus vulcanus and Chroococcidiopsis thermalis. A minimum of seven pigments is required to accurately model the electrochromism of PS I. This study proposes a short list of candidates for the controversial chlorophyll f pigment in FRL C. thermalis that absorbs at 756 nm, and discusses the pros and cons of these assignments. Further experiments are suggested to better understand the functioning of FRL C. thermalis.