pH Dependence of the Donor Side Reactions in Ca2+-Depleted Photosystem II†

Biochemistry ◽  
2003 ◽  
Vol 42 (20) ◽  
pp. 6185-6192 ◽  
Author(s):  
Stenbjörn Styring ◽  
Yashar Feyziyev ◽  
Fikret Mamedov ◽  
Warwick Hillier ◽  
Gerald T. Babcock
Keyword(s):  
Photosystem Ii ◽  
Ph Dependence ◽  
Side Reactions ◽  
Donor Side

Inhibition by Tetranitromethane of Photosynthetic Electron Transport from Water to Photosystem II in Chloroplasts

1980 ◽  
Vol 35 (3-4) ◽  
pp. 293-297 ◽  
Author(s):  
P. V. Sane ◽  
Udo Johanningmeier
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Electron Flow ◽  
Ph Dependence ◽  
Photosynthetic Electron Transport ◽  
Donor Side ◽  
Ps Ii ◽  
Diphenyl Carbazide ◽  
Low Concentrations ◽  
Sh Group

Abstract Low concentrations (10 µM) of tetranitromethane inhibit noncyclic electron transport in spinach chloroplasts. A study of different partial electron transport reactions shows that tetranitromethane primarily interferes with the electron flow from water to PS II. At higher concentrations the oxidation of plastohydroquinone is also inhibited. Because diphenyl carbazide but not Mn2+ ions can donate electrons efficiently to PS II in the presence of tetranitromethane it is suggested that it blocks the donor side of PS II prior to donation of electrons by diphenyl carbazide. The pH dependence of the inhibition by this protein modifying reagent may indicate that a functional-SH group is essential for a protein, which mediates electron transport between the water splitting complex and the reaction center of PS II.

pH Dependence of the Efficiency of Binding of Iron Cations to the Donor Side of Photosystem II

2004 ◽  
Vol 69 (3) ◽  
pp. 331-339 ◽  
Author(s):  
B. K. Semin ◽  
L. N. Davletshina ◽  
A. Yu. Aleksandrov ◽  
V. Yu. Lanchinskaya ◽  
A. A. Novakova ◽  
...  
Keyword(s):  
Photosystem Ii ◽  
Ph Dependence ◽  
Donor Side

scholarly journals Bicarbonate-reversible formate inhibition at the donor side of Photosystem II

1996 ◽  
Vol 1273 (1) ◽  
pp. 1-3 ◽  
Author(s):  
Hanna Wincencjusz ◽  
Suleyman I. Allakhverdiev ◽  
Vyacheslav V. Klimov ◽  
Hans J. van Gorkom
Keyword(s):  
Photosystem Ii ◽  
Donor Side

scholarly journals Expression and pH-dependence of the Photosystem II Subunit S from Arabidopsis thaliana

2010 ◽  
Vol 31 (6) ◽  
pp. 1479-1484 ◽  
Author(s):  
Mi-Suk Jeong ◽  
Eun-Young Hwang ◽  
Gyoung-Ean Jin ◽  
So-Young Park ◽  
Ismayil S. Zulfugarov ◽  
...  
Keyword(s):  
Arabidopsis Thaliana ◽  
Photosystem Ii ◽  
Ph Dependence

scholarly journals Treponema denticola cystalysin exhibits significant alanine racemase activity accompanied by transamination: mechanistic implications1

2003 ◽  
Vol 371 (2) ◽  
pp. 473-483 ◽  
Author(s):  
Mariarita BERTOLDI ◽  
Barbara CELLINI ◽  
Alessandro PAIARDINI ◽  
Martino Di SALVO ◽  
Carla BORRIVOLTATTORNI
Keyword(s):  
Kinetic Parameters ◽  
Binding Sites ◽  
Ph Dependence ◽  
Catalytic Efficiency ◽  
Partition Ratio ◽  
Side Reactions ◽  
Treponema Denticola ◽  
Steady State Kinetic ◽  
Reaction Specificity ◽  
State Kinetic

To obtain information on the reaction specificity of cystalysin from the spirochaete bacterium Treponema denticola, the interaction with l- and d-alanine has been investigated. Binding of both alanine enantiomers leads to the appearance of an external aldimine absorbing at 429nm and of a band absorbing at 498nm, indicative of a quinonoid species. Racemization and transamination reactions were observed to occur with both alanine isomers as substrates. The steady-state kinetic parameters for racemization, kcat and Km, for l-alanine are 1.05±0.03s−1 and 10±1mM respectively, whereas those for d-alanine are 1.4±0.1s−1 and 10±1mM. During the reaction of cystalysin with l- or d-alanine, a time-dependent loss of β-elimination activity occurs concomitantly with the conversion of the pyridoxal 5′-phosphate (PLP) coenzyme into pyridoxamine 5′-phosphate (PMP). The catalytic efficiency of the half-transamination of l-alanine is found to be 5.3×10−5 mM−1·s−1, 5-fold higher when compared with that of d-alanine. The partition ratio between racemization and half-transamination reactions is 2.3×103 for l-alanine and 1.4×104 for d-alanine. The pH dependence of the kinetic parameters for both the reactions shows that the enzyme possesses a single ionizing residue with pK values of 6.5–6.6, which must be unprotonated for catalysis. Addition of pyruvate converts the PMP form of the enzyme back into the PLP form and causes the concomitant recovery of β-elimination activity. In contrast with other PLP enzymes studied so far, but similar to alanine racemases, the apoform of the enzyme abstracted tritium from C4′ of both (4′S)- and (4′R)-[4′-3H]PMP in the presence of pyruvate. Together with molecular modelling of the putative binding sites of l- and d-alanine at the active site of the enzyme, the implications of these studies for the mechanisms of the side reactions catalysed by cystalysin are discussed.

scholarly journals Energetics of the exchangeable quinone, QB, in Photosystem II

2019 ◽  
Vol 116 (39) ◽  
pp. 19458-19463 ◽  
Author(s):  
Sven De Causmaecker ◽  
Jeffrey S. Douglass ◽  
Andrea Fantuzzi ◽  
Wolfgang Nitschke ◽  
A. William Rutherford
Keyword(s):  
Photosystem Ii ◽  
Driving Force ◽  
Energy Gap ◽  
Ph Dependence ◽  
Central Importance ◽  
Paramagnetic Resonance ◽  
Energy Cycle ◽  
The Difference ◽  
Electron Paramagnetic ◽  
Redox Forms

Photosystem II (PSII), the light-driven water/plastoquinone photooxidoreductase, is of central importance in the planetary energy cycle. The product of the reaction, plastohydroquinone (PQH2), is released into the membrane from the QB site, where it is formed. A plastoquinone (PQ) from the membrane pool then binds into the QB site. Despite their functional importance, the thermodynamic properties of the PQ in the QB site, QB, in its different redox forms have received relatively little attention. Here we report the midpoint potentials (Em) of QB in PSII from Thermosynechococcus elongatus using electron paramagnetic resonance (EPR) spectroscopy: Em QB/QB•− ≈ 90 mV, and Em QB•−/QBH2 ≈ 40 mV. These data allow the following conclusions: 1) The semiquinone, QB•−, is stabilized thermodynamically; 2) the resulting Em QB/QBH2 (∼65 mV) is lower than the Em PQ/PQH2 (∼117 mV), and the difference (ΔE ≈ 50 meV) represents the driving force for QBH2 release into the pool; 3) PQ is ∼50× more tightly bound than PQH2; and 4) the difference between the Em QB/QB•− measured here and the Em QA/QA•− from the literature is ∼234 meV, in principle corresponding to the driving force for electron transfer from QA•− to QB. The pH dependence of the thermoluminescence associated with QB•− provided a functional estimate for this energy gap and gave a similar value (≥180 meV). These estimates are larger than the generally accepted value (∼70 meV), and this is discussed. The energetics of QB in PSII are comparable to those in the homologous purple bacterial reaction center.

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