Photochemical Energy Conversion of Far-Red Light in Photosystem I Reaction Centers from Cyanobacterium Acaryochloris marina

Abstract

The conversion of light energy in the near-infrared spectral range by photosynthetic pigment–protein complexes has been intensively studied in recent years in connection with the discovery of cyanobacteria, in the photosynthetic apparatus of which chlorophylls f and d absorbing long-wavelength light are present. Acaryochloris marina occupies a special place among such cyanobacteria. Its photosystem I contains mainly chlorophyll d; it is a part of a special P₇₄₀ pair, the absorption spectrum of which is shifted to the red region by 40 nm. This causes a decrease in the energy of the excited state of P₇₄₀ by ~0.1 eV compared with photosystem I containing chlorophyll a. Complexes of photosystem I from A. marina also have the following peculiarities: four chlorophyll a molecules of the reaction center are replaced by chlorophyll d, and the third pair of chlorophyll a molecules involved in electron transfer are replaced by pheophytin a. The presence of spectrally different cofactors (chlorophyll d and pheophytin a) made it possible to reliably establish the intermediates of primary charge separation reactions in this photosystem I. In this review, we considered the latest results of studies of photochemical energy conversion in the reaction centers of photosystem I of A. marina and possible mechanisms for compensating energy losses of the use of low-energy far-red light for photosynthesis.