Artificial Acceptors and Donors

Hauska, Günter

doi:10.1007/978-3-642-66505-9_18

Cited by 23 publications

(18 citation statements)

References 103 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Since DCMU is present in the assay mixture, the ascorbate must be oxidized by PSI. This is in contrast to most photosynthetic systems examined to date (2,4).…”

Section: Resultscontrasting

confidence: 62%

Direct Spectrophotometric Measurement of Photosystem I and Photosystem II Activities of Photosynthetic Membrane Preparations from Cyanophora paradoxa, Phormidium laminosum, and Spinach

Vernon¹,

Cardon²

1982

Plant Physiol.

View full text Add to dashboard Cite

Vesicles prepared with the French press from membranes of cyanelles of Cyanophora paradoxa retain 02 evolution activity with rates up to 500 micromoles 2,6-dichlorophenolindophenol reduced per hour per milligram chlorophyll. This activity is immediately lost when the vesicles are transferred from the sucrose-phosphate-citrate preparation buffer into dilute phosphate buffer. Similar preparations from Phormidium laminosum, a thermophilic cyanobacterium retain activity under such conditions. Photosystem I activities of both cyanobacterial vesicle preparations were determined by direct spectrophotometric measurement of N,N,N',N'-tetramethyl-p-phenylenediamine photooxidation in the presence of anthraquinone-2-sulfonate. The rates so determined were compared with rates of 02 taken up in the presence of methyl viologen or anthraquinone-2-sulfonate as electron acceptors. The predicted stoichiometry of two was observed for moles of N,N,N',N'-tetramethyl-p-phenylenediamine TMPD is readily reduced by PSII and oxidized by PSI, as shown by the fact that it overcomes DBMIB inhibition of NADP photoreduction coupled to water oxidation (12). In this case, it serves as a bypass for electron flow past the DBMIB inhibition site. In spinach chloroplasts, TMPD reacts with plastocyanin, which serves as a direct donor to PSI (3). In this study we report on the PSII activities of cyanobacterial preparations as well as the direct spectrophotometric measurement of TMPD photooxidation by PSI. The rates observed for PSI in this manner are compared to the rates measured in the traditional way as 02 uptake with excess ascorbate present. The impetus for the study was our interest in the photoreactions of the cyanelle of Cyanophora paradoxa, which although an endosymbiotic organelle, has the photochemical capabilities of cyanobacteria. The lability of the cyanelle PSII is shown as well as the ability of PSI to use ascorbate itself as a donor to a significant extent. This is in contrast to other photosynthetic systems in which ascorbate is a poor donor to PSI (4). MATERIALS AND METHODSSpinach was purchased from a local market. The methods used for growth of C. paradoxa and for isolation of the cyanelle were those previously described (8). The original culture of Phormidium laminosum (OH1-P), a gift from Dr. Richard Castenholz, was grown as described by Jackson and Castenholz (5). Spinach chloroplasts were prepared as previously reported (6) and finally suspended in 0.4 M sorbital and 0.1 M Tris buffer (pH 7.0). Photosynthetically active vesicles were prepared from cyanelles and from P. laminosum cells by treatment in a French Press at 14,000 p.s.i. in the medium described by Dilworth and Gantt (12) which contained 0.5 M sucrose, 0.5 M K-phosphate and 0.3 M sodium citrate, all at pH 7.0. This is designated SPC buffer. Serum albumin was not added, as was previously done by Katoh and Gantt (7). Better activity was observed for PSII if the final vesicle preparation contained 0.2 mg Chl/ml or more.PSII was assayed by DPIP photoreduction in...

show abstract

“…Since DCMU is present in the assay mixture, the ascorbate must be oxidized by PSI. This is in contrast to most photosynthetic systems examined to date (2,4).…”

Section: Resultscontrasting

confidence: 62%

Direct Spectrophotometric Measurement of Photosystem I and Photosystem II Activities of Photosynthetic Membrane Preparations from Cyanophora paradoxa, Phormidium laminosum, and Spinach

Vernon¹,

Cardon²

1982

Plant Physiol.

View full text Add to dashboard Cite

show abstract

“…Moreover, because DPC lowers the A 600 value in the dark, DPC may be directly reducing the DCPIP to a measurable degree. This last point contradicts the suggestion that the rate of direct reduction of DCPIP by DPC is "too slow to interfere" [7] with the DCPIP photoreduction assay and that appropriate dark controls are mandatory.…”

Section: Resultsmentioning

confidence: 72%

Diphenyl carbazide restores electron transport in isolated, illuminated chloroplasts after electron transport from water has been eliminated by mild heat treatment

Dean

Pocock

2004

Biochem Molecular Bio Educ

View full text Add to dashboard Cite

Freshly isolated, illuminated chloroplasts oxidize water and transfer the resulting electrons through the photosynthetic electron transport chains in their thylakoid membranes to the artificial electron acceptor, dichlorophenol indophenol (DCPIP). As a consequence, DCPIP is reduced and the decline in absorbance over time can be used to measure the rate of electron transfer. When gently heated, chloroplasts lose the capacity to oxidize water and the transfer of electrons to DCPIP is eliminated. Electron transport through chloroplasts to DCPIP is restored in the presence of the artificial electron donor diphenylcarbazide (DPC). If students gain experience with the DCPIP photoreduction assay and are given information on normal chloroplast function, they should be able to predict the behavior of heat-treated chloroplasts in a variety of experimental conditions. A number of such predictions are outlined and tested. The experiments can all be conducted with a limited repertoire of equipment and easily prepared solutions. Consequently, this work is well suited to an investigative study in which each student group, in consultation with instructors, can make and test its own prediction. The ways in which changing different variables can affect the quality of the experimental results is emphasized. Additional studies, on measurements of rates of oxygen evolution and emitted chlorophyll fluorescence, are briefly described to support the inferences that heat-treated chloroplasts do not oxidize water and that the vectorial transfer of electrons through them to DCPIP is identical to that in untreated chloroplasts.

show abstract

“…In contrast to the endogenous reaction, MV-supported photophosphorylation was even slightly stimulated by 02 removal. This was not surprising, since the ability of MV to catalyze cyclic photophosphorylation under anaerobic conditions is known (11). Thus, the inhibitor experiments tended to confirm the pseudocycic nature of endogenous photophosphorylation observed in BS cells.…”

Section: Mm) Pi Is Known To Permeate Readily the Envelope Of Spinachmentioning

confidence: 76%

Photophosphorylation in Isolated Maize Bundle Sheath Chloroplasts and Cells

Walker

Izawa²

1980

Plant Physiol.

View full text Add to dashboard Cite

Isolated maize bundle sheath chloroplasts showed substantial rates of noncycic photophosphorylation. A typical rate of phosphorylation coupled to whole-chain electron transport (methylviologen or ferricyanide as acceptor) was 60 pmol per hour per milligram chlorophyll) with a coupling efficiency (P/e2) of 0.6. Partial electron transport reactions driven by photosystem I or II supported phosphorylation with P/e2 values of 0.2 to 03. Thus, two sites of phosphorylation seem to be associated with the photosynthetic chain in much the same way as in spinach chloroplasts.Isolated bundle sheath cells were capable of photosynthetic electron transport with membrane permeant electron carriers (but not with ferfcyanide) at rates which were similar to those found in isolated chloroplasts. ATP formation also occurred during electron transport when ADP and phosphate were present in the cell suspension. The rates of photophosphorylation reactions in cells were about 30 to 40% of those found in isolated chloroplasts (maximum rate in cells 80 imoles ATP per hour per milligram chlorophyll with diaminodurene as electron carrier), with the exception of endogenous photophosphorylation (photophosphorylation without added electron carriers) whose rate was three to four times higher in cells than in chloroplasts. The endogenous photophosphorylation in cells appeared to be coupled to pseudo-cyclic, rather than cyclic, electron transport. It was accompanied by 02 uptake (when the catalase inhibitor KCN was present), was sensitive to dichlorophenyldimethylurea and methylamine, but was totally insensitive to 20 micromolar antimycin which completely inhibited succinate-supported oxidative phosphorylation in the cells. The implications of these and other phenomena associated with photophosphorylation in bundle sheath cells are discussed.It has been assumed that the primary function of maize BS3 chloroplasts is to produce ATP through cyclic photophosphorylation. This concept stems from early observations that "PSIIdeficient" BS chloroplasts were capable of substantial rates of cyclic photophosphorylation (e.g. pyocyanine-mediated) ( (9) and was only partially inhibited by DCMU when exogenous NADPH was present (7).There seems no doubt that BS chloroplasts in vivo have some device with which to meet the high ATP demand (per NADPH) of photosynthesis in BS cells (10). Further characterization of photophosphorylation reactions in BS chloroplasts is necessary before any definitive conclusions can be achieved about the ATP producing reactions in vivo. The importance of such a study is emphasized by the recent finding of Hardt and Kok (8) that the PSII and the whole chain electron transport activities of isolated maize BS chloroplasts can be at least half as high as those of isolated spinach chloroplasts. Our experiments using isolated maize BS cells produced similar results (28). In 02 and proton change experiments with cell suspensions, we also detected a relatively high rate of endogenous pseudocyclic electron flow and an energy-coupling a...

show abstract

Artificial Acceptors and Donors

Cited by 23 publications

References 103 publications

Direct Spectrophotometric Measurement of Photosystem I and Photosystem II Activities of Photosynthetic Membrane Preparations from Cyanophora paradoxa, Phormidium laminosum, and Spinach

Direct Spectrophotometric Measurement of Photosystem I and Photosystem II Activities of Photosynthetic Membrane Preparations from Cyanophora paradoxa, Phormidium laminosum, and Spinach

Diphenyl carbazide restores electron transport in isolated, illuminated chloroplasts after electron transport from water has been eliminated by mild heat treatment

Photophosphorylation in Isolated Maize Bundle Sheath Chloroplasts and Cells

Contact Info

Product

Resources

About