D1-D2-cytochrome b559 complex from the aquatic plant Spirodela oligorrhiza: correlation between complex integrity, spectroscopic properties, photochemical activity, and pigment composition

Abstract

A D1-D2-cyt b559 complex with about four attached chlorophylls and two pheophytins has been isolated from photosystem II of the aquatic plant Spirodela oligorrhiza and used for studying the detergent-induced changes in spectroscopic properties and photochemical activity. Spectral analyses (absorption, CD, and fluorescence) of D1-D2-cyt b559 preparations that were incubated with different concentrations of the detergent Triton X-100 indicate two forms of the D1-D2-cyt b559 complexes. One of them is photochemically active and has an absorption maximum at 676 nm, weak fluorescence at 685 nm, and a strong CD signal. The other is photochemically inactive, with an absorption maximum at 670 nm, strong fluorescence at 679 nm, and much weaker CD. The relative concentrations of the two forms determine the overall spectra of the D1-D2-cyt b559 preparation and can be deduced from the wavelength of the lowest energy absorption band: preparations having maximum absorption at 674, 672, or 670.5 nm have approximately 20, 60, or 85% inactive complexes. The active form contains two chlorophylls with maximum absorption at 679 nm and CD signals at 679 (+) and 669 nm (-). These chlorophylls make a special pair that is identified as the primary electron donor P-680. The calculated separation between the centers of these two pigments (using an extended version of the exciton theory) is about 10 A, the pigments' molecular planes are tilted by about 20 degrees, and their N1-N3 axes are rotated by 150 degrees relative to each other. The other two chlorophylls and one of the two pheophytins in the D1-D2-cyt b559 complex have their maximum absorption at 672 nm, while the maximum absorption of the photochemically active pheophytin is probably at 672-676 nm. During incubation with Triton X-100, the photochemically active complex is transformed into an inactive form with first-order kinetics. In the inactive form the maximum absorption of the 679 nm absorbing Chls is blue-shifted to 669 nm. The first-order decay of the photochemical activity suggests that the isolated D1-D2-cyt b559 complex is stable as an aggregate but becomes unstable on dissociation into individual D1-D2-cyt b559 units.

Characterization of a D1‐D2‐cyt b‐559 complex containing 4 chlorophyll a/2 pheophytin a isolated with the use of MgSO4

“…The absorption spectra of the Dl-D2-cyt b-559 complex containing 4 Chl a/2 Pheo a at 277 and 77 K in 0.1% dodecyl-/I-D-maltoside are shown in Fig. 2 at 277 K exhibit a QY band maximum at 675.5 + 0.3 nm, well in accordance with values reported ealier [3,4,16,24]. p-carotene causes the absorption maximum at 482 2 1 nm; the pheophytin Qx band occurs at 542 + 0.3 nm.…”

“…complexes [1, 3,4]. Our data are also compared with the stoichiometry calculated for a Dl-D2-cyt b-559 complex containing 6 Chl u/2 Pheo a.…”

“…The isolation of this pigment-protein complex has also been described for Pisum sativum [2], Spirodella oligorrhiza [3], Beta vulgaris [4] and Laminaria saccharina [5]. Basically, the method developed by Nanba and Satoh [l] yields, after a long-term Triton X-100 exposure, a PS II RC stoichiometry of 4-5 chlorophyll a, 1 B-carotene and 1 cytochrome b-559 per 2 pheophytin a.…”

“…Basically, the method developed by Nanba and Satoh [l] yields, after a long-term Triton X-100 exposure, a PS II RC stoichiometry of 4-5 chlorophyll a, 1 B-carotene and 1 cytochrome b-559 per 2 pheophytin a. Several reports have shown that the Dl-D2cyt b-559 complex is fairly unstable in the presence of Triton X-100 [3,6] and some alternative methods have been described to obtain more stable preparations [7-lo] which contain 6 chlorophyll a, 2 p-carotene, 1 cytochrome b-559 per 2 pheophytin a. At present, many research groups work with such prepara-tions assuming that the 6 Chl a/2 Pheo a stoichiometry represents the intact Dl-D2-cyt b-559 complex [l l-131.…”

Site-Directed Mutations at D1-His198 and D2-His197 of Photosystem II in Synechocystis PCC 6803: Sites of Primary Charge Separation and Cation and Triplet Stabilization

“…That there are differences in the absorbance spectra for the D1-His198 and the D2-His197 coordinated chlorophylls implies that the exciton coupling between them is quite weak (85-140 cm -1 (13)(14)(15)(16)23)) in contrast to what is observed for the special pair Bchlorophylls of the bacterial reaction centers (500-1000 cm -1 (1, 2)). This observation is consistent with the estimated 10 Å center to center distance between the metal centers of these chlorophylls from electron and X-ray diffraction studies of PSII crystals (17,18,73) as opposed to the 7.6 Å found in bacterial reaction centers (3)(4)(5).…”