Detection of Chlorophyll d′ and Pheophytin a in a Chlorophyll d-Dominating Oxygenic Photosynthetic Prokaryote Acaryochloris marina

Abstract

Sunlight is the ultimate energy source for the earth, and photosynthesis is essential for maintaining almost all life. The primary process of photosynthesis is initiated by photoexcitation and subsequent charge separation at the socalled reaction center (RC).Oxygenic photosynthetic organisms (higher plants, algae and cyanobacteria) have two types of photosystems (PS), according to the nature of the component molecules of the electron acceptor side. 1,2 One is called PS1, possessing Fe-S centers; another is PS2, having quinones.Chlorophyll (Chl) a (Fig. 1) is an essential pigment for oxygenic photosynthesis. However, charge separation is driven by a few special chlorophyll molecules in each RC of PS1 and PS2. Upon excitation, the primary donor pigments reduce the primary acceptor pigments. The primary donors exhibit sharp absorption changes associated with transient oxidation by flash excitation; they are named P700 in PS1 and P680 in PS2, referring to the characteristic peak wavelengths of the absorbance decrease. The primary donor of PS1 has been speculated to be Chl a′, the 13 2 -epimer of Chl a (Fig. 1); 3 the primary acceptor of PS2 is a metal-free Chl a, namely, Phe a ( Fig. 1). 4 In contrast, both the primary donor of PS2 and the primary acceptor of PS1 are apparently normal-type Chl, namely, Chl a.In 1996, a novel oxygenic alga Acaryochloris marina was isolated from a species of colonial ascidians. 5 Although in all previously known organisms capable of oxygenic photosynthesis the dominating chlorophyll is Chl a, the dominating pigment of A. marina is Chl d (Fig. 1). The Chl a content in A. marina is very low, ca. 3% of the Chl d content. [5][6][7] Phycobiliproteins (PBP) are present as antenna in relatively small amounts only. 8,9 Such an unusual pigment composition results in a unique constitution of the photosystems of A. marina. Because isolated PS1 particles showed a flash-induced absorbance loss maximum at ca. 740 nm, the primary donor of PS1 was named P740, 10 corresponding to P700 in other oxygenic photosynthetic organisms. P740 was assumed to consist of Chl d, and not Chl a′. 10The nature of the primary donor of PS2, P680, is still under debate, because it is hard to detect unambiguously the characteristic spectral signal. In comparison with P700 or P740, the data on P680 still remain scanty. Recently, time-resolved florescence spectroscopy in the ps and ns time range on the A. marina cells showed that a delayed fluorescence peak from PS2 was in the Chl a emission range, and not in the wavelength region of Chl d emission;11 hence, the electron donor of PS2 in A. marina was most probably identical with that of other oxygenic photosynthetic organisms, namely, P680 consisting of Chl a. In contrast, information on the primary electron acceptors of PS1 and PS2 in A. marina is so far quite limited.In this paper, we report on the results of a pigment composition analysis of A. marina cells by silica normal-phase HPLC. Chl d′ and Phe a were detected as minor pigments in

18O Labeling of Chlorophyll d in Acaryochloris marina Reveals That Chlorophyll a and Molecular Oxygen Are Precursors

“…1) of Chl d (over 30 nm red-shifted from Chl a) and its very high percentage of total Chls (ϳ95%) are the most striking characteristics of Chl d. Additionally, Acaryochloris exhibits the lowest Chl a content of all aerobic photosynthetic organisms known to date. Containing Chl d as the major photopigment, it would be expected to find Pheo d in significant quantities if it is an intermediate product of major photopigment Chl d. Actually, no Pheo d is detectable in Acaryochloris, which suggests that Pheo d is not involved in photosynthetic reactions of Acaryochloris (33). Furthermore, it supports our hypothesis that Chl d in Acaryochloris is broken down via Chl a.…”

Non‐enzymatic conversion of chlorophyll‐a into chlorophyll‐d in vitro: A model oxidation pathway for chlorophyll‐d biosynthesis

“…and p-toluenesulfonic acid (TsOH, 5 equiv.) in methanol at room temperature for 15 [15][16][17], the above result suggests that the central Mg atom is crucial for the substrate specificity of the enzyme for in vivo conversion of Chl-a into Chl-d.…”

Identification of the special pair of photosystem II in a chlorophyll d -dominated cyanobacterium

“…Pigments were analyzed by HPLC (GULLIVER series; Jasco, Tokyo, Japan) using procedures described elsewhere (41,44), and were detected by a photodiode array detector (MD-915; Jasco). A standard solution containing known amounts of authentic ␣-carotene, Chl a, Chl d, and Phe a was used for quantitative calibration.…”