Shigeki Okayama

Quantitative analysis of membrane components in a highly active O2-evolving photosystem II preparation from spinach chloroplasts

Stoichiometry of membrane components associated with Photosystem II was determined in a highly active O2-evolving Photosystem II preparation isolated from spinach chloroplasts by the treatment with digitonin and Triton X-100. From the analysis with sodium dodecyl sulfate polyacrylamide gel electrophoresis and Triton X-114 phase partitioning, the preparation was shown to contain the reaction center protein (43 kDa), the light-harvesting chlorophyll-protein complex (the main band, 27 kDa), the herbicide-binding protein (32 kDa) and cytochrome b-559 (10 kDa) as hydrophobic proteins, and three proteins (33, 24 and 18 kDa) which probably constitute the O2-evolution enzyme complex as hydrophilic proteins. These proteins were associated stoichiometrically with the Photosystem II reaction center: one Photosystem II reaction center, approx. 200 chlorophyll, one high-potential form of cytochrome b-559, one low-potential form of cytochrome b-559, one 33 kDa protein, one (to two) 24 kDa protein and one (to two) 18 kDa protein. Measurement of fluorescence induction showed the presence of three electron equivalents in the electron acceptor pool on the reducing side of Photosystem II in our preparation. Three molecules of plastoquinone A were detected per 200 chlorophyll molecules with high-performance liquid chromatography. The Photosystem II preparation contained four managanese atoms per 200 chlorophyll molecules.

Redox potential of plastoquinone A in spinach chloroplasts

The redox potential of plastoquinone A in spinach chloroplasts was determined. The midpoint potential of the quinone is about +80 mV at pH 7.0 with an n value of 2. The pH-dependence of the potential is -30 mV per pH between pH 4.0 and 5.7, and -60 mV per pH between pH 5.7 and 8.0. The change of the slope at pH 5.7 is interpreted as the protonation of the oxidized plastoquinone A.

New bile pigment excreted by a Chlamydomonas reinhardtii mutant: A possible breakdown catabolite of chlorophyll a

Summary A chlorophyll b-less mutant of Chlamydomonas reinhardtii excreted new red pigments into the medium accompanying degreening of cells during growth. Accumulation of red pigments in the medium and disappearance of chlorophyll a in algal cells were closely related. A major component (P535) was purified by reversed-phase chromatography, and showed absorption maxima at 535, 385, and 275 nm with shoulders at 570, 500, and 320 nm. Analysis of degradation products by chromic oxidation, together with spectroscopic properties and molecular-mass determination, indicated that P535 bore a structural resemblance to bile pigments characterized by an open tetrapyrrole. It is suggested that the red pigments are probably derived from chlorophyll a.

Electrochemical behavior of ubiquinone and vitamin K incorporated into n-alkanethiol molecular assemblies on a gold electrode

The aim of the present note is to provide information about the effect of the alkyl side chains of ubiquinone and vitamin K on the voltammetric responses of these quinones incorporated into the n-alkanethiol molecular assembles which are modified on the gold electrode

Calvin Benson cycle enzymes in guard-cell protoplasts and their role in stomatal movement.

Summary Calvin-Benson cycle enzymes were found in Vicia guard-cell protoplasts. On the basis of enzyme activities and rates of photosynthetic O2 evolution in guard-cell and mesophyll protoplasts, we conclude that guard-cell chloroplasts utilize largely the phosphoglycerate (PGA)/dihydroxyacetone phosphate (DHAP) shuttle for the transfer of ATP and reducing equivalents from chloroplasts to the cytosol. In guard cells, PGA formation by photosynthetic CO2 fixation may act as a starter of the PGA/DHAP shuttle across the chloroplast envelope in synchronization with the photophosphorylation, thereby driving the stomatal opening.

Photochemical Oxidation and Reduction of Plastoquinone sensitized by Isolated Chlorophylls

SINCE the discovery of plastoquinone in chloroplasts by Crane1,2, many investigations have been reported on the role of the quinone in photosynthesis. Bishop3 showed that the quinone participated in the photolysis of water. Krogmann4 and Krogmann and Olivero5 demonstrated the indispensability of the quinone as a co-factor for photophosphorylation. Crane et al.6 and Redfearn and Friend7 observed photo-induced reduction and dark reoxidation of the quinone in chloroplasts. The localization of plastoquinone in the electron transport system of photosynthesis was verified by Witts school8,9. They indicated that the quinone acted as a primary electron acceptor from photochemically reduced chlorophyll a. Since all these investigations were carried out with chloroplasts, no evidence has been presented showing the direct interaction of plastoquinone with chlorophylls. Tollin and Green10 observed electron paramagnetic resonance signals, showing the light-induced single electron transfer reactions between chlorophyll a and various kinds of quinones, but plastoquinone was not included among the quinones they used. In this communication, we present evidence indicating that plastoquinone can be oxidized or reduced photochemically in the presence of chlorophyll a or b.

STUDIES ON QUINONES IN GREEN LEAVES

Publisher Summary This chapter presents the studies on quinones in green leaves. Green leaves contain plastoquinone (PQ). PQ functions as the primary and the secondary electron acceptors of photosystem II (PS-II), and the electron and proton carrier (A) between the two photosystems. The PQ content in chloroplasts is a mixture of several homologues, PQ A, B, and C. PQB and PQC are mixtures of six different homologues called PQB1 to PQB6 and PQC1 to PQC6, respectively. These homologues cannot be distinguished from each other by spectrophotometric methods. Therefore, it is necessary to separate each homologue chromatographically before spectrophotometric analysis. This study revealed that PQA is the only homologue in the oxygen-evolving PS-II particles by analysis with high performance liquid chromatography. Various functions of PQ might be because of PQA in different molecular environments.

Inhibition of the light-induced H+ release from uncoupled thylakoid membranes by N-ethylmaleimide

The light-induced H+ release from thylakoids, which can be observed under completely uncoupled conditions, was inhibited by the SH reagent N-ethylmaleimide (NEM) and its analogs, while the conventional H+ uptake and electron transfer were not affected. The half-inhibiting concentration of NEM for the H+ release was 10 mM and 4 mM in thylakoids in the presence of nigericin and in CF1-depleted thylakoids, respectively. The inhibitory effect increased with the increase in hydrophobicity of the NEM analogs: N-methylmaleimide less than N-ethylmaleimide less than N-phenylmaleimide. It is suggested that SH groups in hydrophobic interior within the membrane are essential to the release of protons.