Electron transport spinach

The first cytochrome to be recognised as a component of the photosynthetic electron transport chain was cytochrome f [142]. The properties of cytochrome f have been reviewed [143,144], and amino-acid sequence information is available for pea, spinach, wheat and tobacco [145]. The axial ligand to the heme-Fe... 

The exploratory studies, as conducted, did not distinguish between effects Imposed on the stromal-associated CO2 fixation (Calvin cycle) reactions or on the light reactions associated with the thylakoids. Consequently, studies were conducted on light-induced electron transport and ATP synthesis associated with isolated spinach thylakold membranes. 

Chloroplasts, of Coupled Electron Transport and Phosphorylation, and of Uncoupled Electron Transport by Spinach Thylakoids... 

Figure 1. Representative polarographic traces that depict inhibition by energy transfer inhibitors and allelochemicals of ADP-stimulated electron transport in isolated spinach thylakoids and circumvention of the inhibition by an uncoupler (FCCP, 2 pM). Trace A chlorotributyltin (TBT, 1 pM) trace B phlorizin (400 pM) trace C DCCD (20 pM) trace D quercetin (200 pM) trace E naringenin (1 mM). Water served as electron donor and methyl viologen as electron acceptor. Rates of oxygen utilization, that resulted from the autooxidation of methyl viologen, expressed as pmol 0 consumed/mg Chi h, are indicated parenthet ically.

The biological functions of chloroplast ferredoxins are to mediate electron transport in the photosynthetic reaction. These ferredoxins receive electrons from light-excited chlorophyll, and reduce NADP in the presence of ferredoxin-NADPH reductase (23). Another function of chloroplast ferredoxins is the formation oT" ATP in oxygen-evolving noncyclic photophosphorylation (24). With respect to the photoreduction of NADP, it is known that microbial ferredoxins from C. pasteurianum (16) are capable of replacing the spinach ferredoxin, indicating the functional similarities of ferredoxins from completely different sources. The functions of chloroplast ferredoxins in photosynthesis and the properties of these ferredoxin proteins have been reviewed in detail by Orme-Johnson (2), Buchanan and Arnon (3), Bishop (25), and Yocum et al. ( ). 

Reaction of 232 with 4-substituted l,3-oxazol-5(4/7)-one 247 led to diacylhydrazines 248 or to imidazole derivatives 249 depending on the reaction temperature (Scheme 24). l,2,4-Triazole-3-thione 250 was obtained by a two-step sequence from 232 with phenyl isothiocyanate and subsequent base-catalyzed cyclization of thiosemicarbazide 251. The effects of hydrazones 241-246 on inhibition of photosynthetic electron transport in spinach chloroplasts and chlorophyll content in the antialgal suspensions of Chlorella vulgaris were investigated <2005CEC622>. 

Rojas, I. S., Lotina-Hennsen, B., and Mata, R., 2000. Effect of lichen metabolites on thylakoid electron transport and photophosphorylation in isolated spinach chloroplasts. J. Nat. Prod 63, 1396-1399. 

Photosystem II. Spinach and pea PSII particles coated on different Ti02 based electrodes were used for photocurrent measurements in the presence of PSII electron acceptor DMBQ. In all experiments, addition of DMBQ resulted in an increase in photocurrent which remained constant for long periods. In control experiments with no deposition of PSII on the electrodes, there was no change in the photocurrent pattern on addition of DMBQ. Addition of the PSII oxygen evolution inhibitor DCMU caused an immediate fall in photocurrent, suggesting that the electron transport to the Ti02 electrode is linked to water photolysis. 

Berthold, D.A., Babcock G.T. and Yocum C.F. 1981. A highly resolved, oxygenevolving photosystem II preparation from spinach thylakoid membranes. EPR and electron transport properties. FEBS Lett. 134,231-234. 

Melis A. and Anderson J.M. (1983). Structural and functional organization of the photosystems in spinach chloroplasts antenna size, relative electron transport capacity, and chlorophyll composition. Biochim. Biophys. Acta 724, 473-484. 

Melis A, Spangfort M and Andersson B. (1987). Light-absorption and electron transport balance between photosystem-II and photosystem-I in spinach chloroplasts. Photochem. Photobiol. 45, 129-136. 

Fig. 7. (A) Reaction scheme involving a cyclic electron transport around photosystem I mediated by the TMPDVTMPD couple. (B) Semi-logarithmic plots of decay of absorbance changes at 700 and 575 nm in spinach D144 particles following a flash at different TMPD concentrations [TMPD at 67 pM o for 0.2 pM, for 0.6 pM, and for 1.2 pM TMPD, respectively] Figure source (B) Hiyama and Ke (1972) Difference spectra and extinction coefficient of P700. Biochim Biophys Acta 267 162.

RK Chain (1985) Involvement ofplastoquinone and lipids in electron transport reactions mediated by the cytochrome bg-f complex isolated from spinach. FEES Lett 180 321-325... 

ATP synthesis in photosynthetic organisms, i.e., photophosphorylation, was discovered nearly fifty years ago. In 1954 Albert Frenkel" using membrane vesicles of purple bacteria, and Daniel Arnon and coworkers, using spinach chloroplasts, reported light-induced phosphorylation almost simultaneously and opened up a new era in photosynthesis research. These investigations not only established the conditions necessary for ATP synthesis by photosynthetic membranes, but also established that ATP synthesis is closely related to electron transport. 

Larkum, A. W., Boardman, N. K. FEBS Letters 40 (1), 229 (1974). The effect of nigericin and valinomycin on CO2 fixation electron transport and P518 in intact spinach chlorplasts... 

Foyer CH and Lelandais M (1996) A comparison ofthe relative rates of transport of ascorbate and glucose across the thylakoid, chloroplast and plasmalemma membranes of pea leaf mesophyll cells. J Plant Physiol 148 391-398 Foyer CH, Rowell J and Walker D (1983) Measurement ofthe ascorbate content of spinach leaf protoplasts and chloroplasts during illumination. Planta 157 239-244 Foyer CH, Furbank R, Harbinson J and Horton P (1990) The mechanisms contributing to photosynthetic control of electron transport by carbon assimilation in leaves. Photosynth Res 25 83-100... 

Vierke G, Struckmeier P. Binding of copper (II) to protein of the photosyntheric membrane and its correlation with inhibition of electron transport in class II chloroplasts of spinach. Z Naturforsch C 1977 32(7-8) 605-610. 

Shown in Table II are I q values for inhibition of electron transport in spinach thylakoids (water to ferricyanide) and the associated phosphorylation reaction by the test compounds. Also included are I5Q values for inhibition of the light-dependent quenching of atebrin fluorescence and the ratio obtained by dividing the Icq for the atebrin response by the I q for inhibition of photophosphorylation. The relative order of inhibitory potency for some of the compounds for inhibition of ferricyanide reduction has been reported previously (12). For the herbicides,... 

The more widespread route of catabolism could be via reaction 2. This is an extremely important reaction in higher plants as it is considered to be the primary source of CO2 in photorespiration (cf. Tolbert, this series, Vol. 2, Chapter 12 Keys, this volume. Chapter 9 Lorimer, Chapter 9, Vol. 8 this treatise). Reaction 2 can be carried out by particles from leaves of spinach (Kisaki et al., 1971) or tobacco (Bird et al., 1972a,b), and by pea cotyledon mitochondria (Clandinin and Cossins, 1975). There are some differences between the various systems in regard to the effect of oxygen and exogenous cofactors. The spinach and pea systems are stimulated by the addition of NAD, pyridoxal phosphate, and tetrahydrofolic acid. The tobacco leaf system does not require these exogenous cofactors however, electrons transported during the reaction can be linked to ATP synthesis with three ATP... 

More recently Huang and Cavalieri (1979) have studied a similar enzyme in mitochondria isolated from spinach leaves. This enzyme had a pH optimum at 8.0-8.5 with a A , for proline of 28 mAf. The enzyme was linked to the mitochondrial electron transport system and MgCl2 and flavin adenine dinucleotide were required for maximal activity. The spinach oxidase also was inactive after Triton X-100 treatment. 

CX>2 fixation, 20 M DEMIB (8) was used. In the presence of both DBMIB and OyiQ, addition of 10 itiM H003 to the depleted sairple also stimulated the electron transport rate by a factor of 4. A maximum HOO3" effect was found at approximately pH 6.7 (Fig. 5). This result is consistent with the conclusion that both CO2 and HOO3", not OO2 or CX)3"" alone, may be the active species in the stimulation of Hill reaction. Blubaugh and Govindjee (9) have shown that HC3O3 is the active species involved in spinach thylakoids. 

Photosynthetic Electron Transport. Thylakoids were isolated from spinach leaves by the method of Whitmarsh (13). Chlorophyll content was measured according to Arnon (14). The reaction medium contained 0.1 M sorbitol, 10 mM MgCl2, 10 mM NaCl, 10 mM Tricine-NaOH (pH 7.8) 0.05 mM Dichlorophenol-indophenol (DCPIP), 1 mM NH4C1, 1 pM Gramicidin D and thylakoid membranes equivalent to 5 pg chlorophyll/ml. Triplicate readings were taken 0, 15 and 30 s after illumination at 580 nM and initial rates were calculated over a range of inhibitor concentrations. ... 

Incubation of leaf discs in LY181977 causes an increase in chlorophyll fluorescence similar to that caused by atrazine and diuron (Figure 2). Similarly the IC50 for DCPIP reduction by isolated spinach thylakoids is similar for LY181977 (0.73 pM) and atrazine (0.36 pM). This indicates that LY181977 inhibits photosynthetic electron transport through photosystem II with efficacy similar to that of atrazine. 

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