Subchloroplast particles

The primary acceptor in PS II is a plastoquinone, PQ, as ascertained from optical absorbance difference spectroscopy [46], Until recently, the EPR spectrum of the semiquinone escaped observation, and only the advent of preparation methods for PS II subchloroplast particles made its recording possible. As surmised earlier, the spectrum of the intact acceptor [47] very much resembled the very broad qui-none-iron acceptor complex in purple bacteria, whereas in iron-depleted PS II particles the narrow spectrum typical of an immobilized semiquinone was found [48], As in the bacterial photosystem, flash-induced reduction of Q, of the second quinone, Qb, or of both resulted in somewhat different EPR spectra, indicative of structural changes that influence the magnetic interaction between the semiquinone and the non, and/or between the two semiquinones [49],... 

Direct evidence for the chemiosmotic theory [1] is proton motive ATP synthesis in purified FgFj proteoliposomes on applying [38,131]. Jagendorf and Uribe [132] first demonstrated ATP synthesis in subchloroplast particles that had been loaded with a weak acid (pH 4.5) and were then transferred to alkaline media at pH values... 

Fig. 6. Cytochrome bS59 photooxidation in spinach chioropiasts (A), photoreduction in TSF2a particles (B) and in D1/D2/Cyt bS59 complex (C). See text for discussion. Figure (A) from Knaff and Arnon (1969) Light-induced oxidation of chloroplast b-type cytochrome at-189 °C. Proc Nat Acad Sci, USA 63 959, 960 (B) Ke, Vernon and Cheney (1972) Photoreduction of cytochrome b5S9 in a photosystem-ll subchloroplast particle. Biochim Biophys Acta 256 350 (C) Barber and De Las Rivas (1993) A functional model for the role of cytochrome (3559 in the protection against donor and acceptor side photoinhibition. Proc Nat Acad Sci, USA 90 10943, 10944.

B Ke, LP Vernon and TH Chaney (1972) Photoreduction of cytochrome b559 in a photosystem II subchloroplast particle. Biochim Biophys Acta 256 245-357... 

Fig. 6. (A) Effect of composition of a binary soivent mixture on the apparent Chi a Aotal chlorophyli moiar ratio in extracts of spinach leaf tissue (0) and chloroplasts ( ). (B) relationship between the Chi a/Chl a molar ratio and the Chi a/P700 molar ratio for a number of P700-enriched subchloroplast particles by chloroform extraction (o) and by acetone extraction ( ). The solid line ciosest to the open circles is for Chi aVP700=1 and that nearest the filled circles for Chi aVP700= 2. See text for details. Figure source (A) Watanabe, Kobayashi, Maeda, Oba, Yoshida, Van de Meent and Amesz (1992) Function of the C13 -epimer chlorophylls in type I photosystem reaction centers. In N Murata (ed) Research In Photosynthesis, Vol III 4. Kluwer Acad PubI (B) Maeda, Watanabe, Kobayashi and Ikegami (1992) Presence of two chlorophyll a molecules at the core of photosystem I. Biochim Biophys Acta 1099 78.

RA Baker and EC Weaver (1973) A correlation ofEPR spins with P in spinach subchloroplast particles. Photochem Photobiol 18 237-241... 

P S0tifand P Mathis (1980) The oxidation-reduction potential of P-700 in chloroplast lamellae and subchloroplast particles. Arch Biochem Biophys 204 477-485... 

Fig. 2. EPR spectra (measured at 13 K) of the subchloroplast particle TSF-I dark-adapted and frozen in the dark (top spectrum) and the same sample subsequently illuminated at 13 K. Unpublished results of B Ke and H Beinert (1972).

Fig. 4. (A) EPR spectra at 13 K of TSF-I subchloroplast particles at different stages of a reductive titration (B) Plot of EPR-signal amplitudes of four prominent lines for redox titrations at pHs 10 and 9. Open circles in the right panel represent the total signal amplitude generated by a combination of chemical reduction at room temperature and subsequent illumination at 77 K. Figure source Ke, Hansen and Beinert (1973) Oxidation-reduction potentiais of bound iron-suifur proteins of photosystem t. Proc Nat Acad Sci, USA 70 2042, 2043.

Cammack and Evans used another approach to investigate the FeS-A and FeS-B iron-sulfur proteins. They used guanidine.HCl in dimethylsulfoxide (DMSO) to reversibly unfold the polypeptide chain and at the same time maintain the iron-sulfur clusters intact. Their treatment of a PS-I subchloroplast particle... 

AR McIntosh, M Chu and JR Bolton (1975) Flash photolysis electron spin resonance studies of the electron acceptor species at low temperatures in photosystem I of spinach subchloroplast particles. Biochim Biophys Acta 376 308-314... 

Apparently, light-induced paraquat reduction and STibsequent peroxidation is also achieved without electron transport, e.g., in subchloroplast particles where endogenous substrates or chlorophyll itself may be the electron donors (22.) Similar peroxidative processes are induced by diquat ( S). 

PHOTOREACTIVATION AND PHOTO INACTIVATION OF PHOTOSYSTEM II AFTER A COMPLETE REMOVAL OF MANGANESE FROM PEA SUBCHLOROPLAST PARTICLES... 

Schemes of electron transfer interactions of FNR in thylakoid membranes are deduced mainly from experimental results obtained in model systems (reviewed in 1). Pioneering works by Bouges-Bocquet (4), who studied flash-induced transient of FNR in algal cells, has not tDeen followed by systematic investigations in isolated chloroplasts and thylakoid membranes. In algal cells, ambiguity arises from intense light scattering (5). Low permeability of the cell wall also restricts the use of inhibitors, ionophores, artificial acceptors and substrates. It is consequently necessary to confirm and extend these earlier studies using isolated thylakoid membranes and/or subchloroplast particles.

Lien S, Racker E (1971) Partial resolution of the enzymes catalyzing photophos- phorylation. VIII Properties of silicotungstate-treated subchloroplast particles. J. Biol. Chem. 246, 4298-4307... 

Olsen LF and Cox RP (1982) Transient kinetics of the reaction between cytochrome -552 or plastocyanin and P700 in subchloroplast particles, Biochim. Biophys. Acta 679, 436-443. 

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