Characterization of Highly Purified Photosystem I Complexes from the Chlorophyll d-dominated Cyanobacterium Acaryochloris marina MBIC 11017

Abstract

Photochemically active photosystem (PS)IIn addition to P740, the difference spectrum contained an additional band at 728 nm. The redox potentials of P740 were estimated to be 439 mV by spectroelectrochemistry; this value was comparable with the potential of P700 in other cyanobacteria and higher plants. This suggests that the overall energetics of the PS I reaction were adjusted to the electron acceptor side to utilize the lower light energy gained by P740. The distribution of charge in P740 was estimated by a density functional theory calculation, and a partial localization of charge was predicted to P1 Chl (special pair Chl on PsaA). Based on differences in the protein matrix and optical properties of P740, construction of the PS I core in A. marina was discussed.

Spectroelectrochemical determination of the redox potential of pheophytina, the primary electron acceptor in photosystem II

“…The standard deviation of 6 mV for the determination of E m (Phe a/Phe a Ϫ ) seems to be rather large (seen in Fig. S2), especially compared with our previous measurements on redox species in PS I and II yielding values within an error range of Ϯ2 mV (27)(28)(29)(30)(31); this might be partially due to an interference from irreversible photoreactions of peripheral species during photoaccumulation of Phe a Ϫ . The E m (Phe a/Phe a Ϫ ) determined in the present work is by as much as Ϸ100 mV positive of those reported in 1978-1981, namely Ϫ610 Ϯ 30 mV by Klimov et al…”

“…These features enabled us to determine the redox potential E m of P700 (primary donor in PS I) and other components to within Ϯ2 mV (27)(28)(29)(30)(31) and to unveil the species dependence of the E m value of P700 (28,29). This has been extended in the present work to measure the E m (Phe a/Phe a Ϫ ) value in PS II complexes at physiological pH, by overcoming several difficulties inherent in the strongly negative potential range.…”

Redox potentials of primary electron acceptor quinone molecule (Q A ) − and conserved energetics of photosystem II in cyanobacteria with chlorophyll a and chlorophyll d

“…In PS I, the redox potential of P740 (corresponding to P700 for other oxygenic photosynthetic organisms) is the same as that of P700 (6,13), suggesting that no specific mechanism exists to compensate for the lower energy from the longer wavelength absorption of Chl d. Thus, one can conclude that the redox potentials of the special pair in oxygenic photosynthetic organisms are determined by the oxidizing side of the PS and not by the reducing side. These considerations suggest that a determining factor for the potential of the special pair with a specific pigment(s) might be related to an oxidation reaction that includes ligands and/or hydrogen bonds from the amino acid(s) of proteins to the pigments.…”

“…Since the discovery of Chl d in Acaryochloris marina in 1996 (3,4), questions have arisen on the whether the electron transfer system in this organism is significantly different from those with Chl a. Interestingly, the functional "special pair" are Chl d molecules in the reaction centers of PS I and II in A. marina (5,6); however, in PS II, Phe a is the primary electron acceptor. Chl d gains light energy at longer wavelengths and with a lowered redox potential, by ∼80 mV, compared with that of Chl a in Synechocystis sp.…”

Novel chlorophylls and new directions in photosynthesis research

“…A recent study investigating the redox potential of the Chl d special pairs in A. marina reported no differences for the redox potential level between Chl a-containing cyanobacteria and A. marina (Allakhverdiev et al 2010;Allakhverdiev et al 2011). For PSII reaction centre in A. marina, there is general agreement that Chl a is replaced by Chl d, at least at accessory sites (Chl D1 and Chl D2 ) Tomo et al 2007) and Pheo a (instead of Pheo d) is the primary acceptor of D1-side as in other oygenic photosynthetic organisms (Tomo et al 2007(Tomo et al , 2008. However, a controversy over the identities of the special pair chlorophylls in RC II has been debated more than 10 years due to the lack of the purified PSII reaction centre complexes Itoh et al 2007;Tomo et al 2007).…”