Inhibitory Effects of Synthetic Lanthanum-Crown Ether at the Reducing Side of Photosystem II

1998 ◽  
Vol 53 (1-2) ◽  
pp. 49-54
Author(s):  
Surendra Chandra Sabat ◽  
Subash Padhye ◽  
Prasanna Mohanty
Keyword(s):  
Electron Flow ◽  
Hill Coefficient ◽  
Inhibitory Effects ◽  
Ps Ii ◽  
Binding Domains ◽  
Acceptor Side ◽  
Plot Analysis ◽  
Number Of Binding Sites ◽  
Straight Lines ◽  
The Hill

Abstract Inhibitory effects of lanthanum-crown [La-(Pic)3 (15-crown-6) 3H2O].was investigated on the O2 evolution activity of photsystem II particles. Lanthanum (La)-crown inhibited the electron flow at the reducing side of PS II complex. Short duration (1-2 min) treatment of PS II membranes with trypsin partly developed resistance to La-crown inhibition. However, longer proteolytic treatment (>2 min) appeared to expose newer site(s) for La-crown inhibi­tion. The inhibitory constant (Ki) for La-crown was nearly 0.17 | μᴍ . This inhibitory capacity is about 4 to 5 times less than the potent PS II inhibitor diuron which also binds at the acceptor side of PS II. The number of binding sites for La-crown was found to be 1 per 20 chlorophyll molecules. The Hill plot analysis showed the presence of three distinct straight lines suggesting that the compound acts at least at three sites. Furthermore, from the slope value (Hill coefficient) it is suggested that two of these sites provide minimum of two binding domains for the inhibitor.

scholarly journals Absence of positive co-operativity in the binding of 2,3,7,8-tetrachlorodibenzo-p-dioxin to its cytosolic receptor protein

1987 ◽  
Vol 244 (3) ◽  
pp. 539-546 ◽  
Author(s):  
K Farrell ◽  
S Safe
Keyword(s):  
Hill Coefficient ◽  
Receptor Protein ◽  
Ah Receptor ◽  
Nonspecific Binding ◽  
Binding Studies ◽  
Hill Plot ◽  
Plot Analysis ◽  
Tetrachlorodibenzo P Dioxin ◽  
High Level ◽  
The Hill

The role of positive co-operativity in stabilizing the binding of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to the rat hepatic cytosolic TCDD receptor protein (Ah receptor) was investigated. The binding mechanism of TCDD was determined by kinetic means through equilibrium and saturation binding studies, and Scatchard and Hill plot analysis. In all studies, the slope of the Hill plot was close to 1.0, indicating the absence of positive co-operativity. Interpretation of the Scatchard plot was however complicated by the fact that both linear and nonlinear plots were experimentally obtained. The nonlinearity was shown to be an experimental artifact and a consequence not of co-operativity, but of high levels of nonspecific binding. The high level of nonspecific binding could be attributed to: (1) lipophilicity of the TCDD ligand, and (2) inefficient competition of receptor-bound [3H]TCDD. When nonspecific binding was minimized, the Scatchard slope was linear and in agreement with the Hill coefficient, thus indicating the lack of positive co-operativity in the binding of TCDD to the Ah receptor.

Effect of an Antiserum to a Thylakoid Membrane Polypeptide on the Primary Photoreaction of Photosystem II

1976 ◽  
Vol 31 (9-10) ◽  
pp. 594-600 ◽  
Author(s):  
Georg H. Schmid ◽  
Gernot Renger ◽  
Michael Gläser ◽  
Friederike Koenig ◽  
Alfons Radunz ◽  
...  
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Photosystem I ◽  
Electron Flow ◽  
Primary Electron ◽  
Hill Reaction ◽  
Ps Ii ◽  
Absorption Change ◽  
Oxygen Evolving ◽  
The Hill

Abstract As was described previously, an antiserum to polypeptide 11000 inhibited photosynthetic elec­tron transport on the oxygen evolving side of photosystem II. The effect of the antiserum on chloro­plasts from two tobacco mutants also clearly showed that the inhibition site is on the photosystem II-side of the electron transport chain. One of the two tobacco mutants lades the oxygen evolving capacity but exhibits some electron transport with tetramethyl benzidine, an artificial donor to PS II. In this mutant electron transport was barely inhibited. The effect of the antiserum on the primary photoevents showed that the initial amplitude of the absorption change of chlorophyll an at 690 nm and that of the primary electron acceptor X320 at 334 nm both diminished in the presence of the antiserum. Both signals were restored upon addition of diphenylcarbazide another artificial donor to photosystem II. Comparison of the degree of inhibition on the amplitudes of the fast and slow components of the 690 nm absorption change with the manometrically measured inhibition of electron transport shows that besides a full inactivation of a part of the reaction centers of photosystem II another part apparently mediates a fast cyclic electron flow around photosystem II as reported by Renger and Wolff earlier for tris-treated chloroplasts. Moreover, the antiserum affects the low temperature fluorescence in a way which is opposite to Murata’s effect of the Mg2+ -ion induced inhibition of energy spill-over from photosystem II to photosystem I. The antiserum under the condition in which the Hill reaction is inhibited lowered the 686 nm emission and enhanced the 732 nm emission which indicates an enhanced energy spill-over to photosystem I.

On the Requirement of Bound Bicarbonate for Photosystem II Activity

1997 ◽  
Vol 52 (1-2) ◽  
pp. 24-32 ◽  
Author(s):  
◽  
C. Xu ◽  
J. J. S. van Rensen
Keyword(s):  
Side Effects ◽  
Photosystem Ii ◽  
Electron Flow ◽  
Residual Activity ◽  
Fluorescence Yield ◽  
Donor Side ◽  
Ps Ii ◽  
Acceptor Side ◽  
Infrared Gas Analyser ◽  
Photosystem Ii Activity

Abstract In photosystem II of plants and cyanobacteria, but not in reaction centers of anoxygenic photosynthetic bacteria, formate is known to inhibit electron flow which is reversed fully upon bicarbonate addition. At issue has been an old controversy whether this effect is on the acceptor or the donor side of photosystem II (PS II). We present here data on chloroplast thylakoids for donor side effects, that is accompanied by acceptor side effects, from measurements on chlorophyll a fluorescence yield changes after light flashes 1-6. Further, sensitive differential infrared gas analyser measurements show that bicarbonate is indeed bound in both maize and pea thylakoid suspensions depleted of CO2 without any inhibitor; here, high rates of electron flow are associated with the presence of a maximum of 0.8 to 1.25 (corrected for residual activity) CO2 per photosystem II reaction center. It is suggested that bicarbonate bound to the acceptor side is required for photosystem II activity , both on the acceptor and the donor sides in the same experiment and in the same sample.

Pentachlorophenol Inhibits Photosynthetic Electron Flow and Quenches Chlorophyll Fluorescence after Preillumination

1986 ◽  
Vol 41 (4) ◽  
pp. 433-436 ◽  
Author(s):  
Christof Niehrs ◽  
Jan Ahlers
Keyword(s):  
Chlorophyll Fluorescence ◽  
Electron Transport ◽  
Electron Flow ◽  
Hill Reaction ◽  
Light Requirement ◽  
Ps Ii ◽  
Photosynthetic Electron Flow ◽  
Fluorescence Quench ◽  
The Common ◽  
The Hill

The pesticide PCP was shown to inhibit the Hill reaction in broken chloroplasts (I50 = 15 μᴍ) and to quench chlorophyll fluorescence. Both effects require preillumination. In contrast to the common “phenol-type” inhibitors, neither inhibition of Hill reaction nor chlorophyll fluorescence quench were affected by pretreatment of chloroplast with trypsin instead of preillumination. An inhibition site differing from the “phenol type” inhibitors is therefore assumed. The results presented indicate that the observed light requirement is due to electron transport through PS II. Measurements of intrinsic tryptophane fluorescence relate the PCP site of binding to a hydro- phobic environment.

scholarly journals Kinetics of hexokinase D (‘glucokinase’) with inosine triphosphate as phosphate donor. Loss of kinetic co-operativity with respect to glucose

1987 ◽  
Vol 245 (3) ◽  
pp. 625-629 ◽  
Author(s):  
D Pollard-Knight ◽  
A Cornish-Bowden
Keyword(s):  
High Glucose ◽  
Kinetic Models ◽  
Binding Sites ◽  
Ternary Complex ◽  
Hill Coefficient ◽  
Phosphate Donor ◽  
Km Value ◽  
Number Of Binding Sites ◽  
The Hill ◽  
Kinetics Of

When ATP, the normal phosphate donor for hexokinase D (‘glucokinase’), is replaced by ITP, the positive co-operativity with respect to glucose disappears. This may be rationalized in relation to kinetic models for hexokinase D co-operativity, which assume that with the normal substrates the chemical reaction and subsequent release of products occur so rapidly that binding of substrates cannot approach equilibrium and is therefore not constrained by the thermodynamic requirement that the Hill coefficient for substrate binding cannot exceed the number of binding sites. ITP is a much poorer substrate than ATP, however: its Km value at high glucose concentrations is 24 times the value for ATP, whereas the value of the limiting rate V is decreased about 8-fold. Consequently it is no longer possible for the ternary complex to be converted into products rapidly enough to generate kinetic co-operativity. The negative co-operativity with respect to glucose observed in 2H2O with ATP as phosphate donor also disappears when ITP is used instead of ATP.

On the Measurement of Cooperativity and the Physico-Chemical Meaning of the Hill Coefficient

2019 ◽  
Vol 20 (9) ◽  
pp. 861-872 ◽  
Author(s):  
Andrea Bellelli ◽  
Emanuele Caglioti
Keyword(s):  
Ligand Binding ◽  
Hormone Receptors ◽  
Fundamental Property ◽  
Statistical Correlation ◽  
Hill Coefficient ◽  
Biological Macromolecules ◽  
Physico Chemical ◽  
Physiological Relevance ◽  
Minimum Estimate ◽  
The Hill

Cooperative ligand binding is a fundamental property of many biological macromolecules, notably transport proteins, hormone receptors, and enzymes. Positive homotropic cooperativity, the form of cooperativity that has greatest physiological relevance, causes the ligand affinity to increase as ligation proceeds, thus increasing the steepness of the ligand-binding isotherm. The measurement of the extent of cooperativity has proven difficult, and the most commonly employed marker of cooperativity, the Hill coefficient, originates from a structural hypothesis that has long been disproved. However, a wealth of relevant biochemical data has been interpreted using the Hill coefficient and is being used in studies on evolution and comparative physiology. Even a cursory analysis of the pertinent literature shows that several authors tried to derive more sound biochemical information from the Hill coefficient, often unaware of each other. As a result, a perplexing array of equations interpreting the Hill coefficient is available in the literature, each responding to specific simplifications or assumptions. In this work, we summarize and try to order these attempts, and demonstrate that the Hill coefficient (i) provides a minimum estimate of the free energy of interaction, the other parameter used to measure cooperativity, and (ii) bears a robust statistical correlation to the population of incompletely saturated ligation intermediates. Our aim is to critically evaluate the different analyses that have been advanced to provide a physical meaning to the Hill coefficient, and possibly to select the most reliable ones to be used in comparative studies that may make use of the extensive but elusive information available in the literature.

Interaction of Photosystem II Herbicides with Bicarbonate and Formate in Their Effects on Photosynthetic Electron Flow

1984 ◽  
Vol 39 (5) ◽  
pp. 374-377 ◽  
Author(s):  
J. J. S. van Rensen
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Electron Flow ◽  
Photosynthetic Electron Transport ◽  
Hill Reaction ◽  
Amaranthus Hybridus ◽  
Apparent Affinity ◽  
Photosynthetic Electron Flow ◽  
Different Characteristics ◽  
The Hill

The reactivation of the Hill reaction in CO2-depleted broken chloroplasts by various concentrations of bicarbonate was measured in the absence and in the presence of photosystem II herbicides. It appears that these herbicides decrease the apparent affinity of the thylakoid membrane for bicarbonate. Different characteristics of bicarbonate binding were observed in chloroplasts of triazine-resistant Amaranthus hybridus compared to the triazine-sensitive biotype. It is concluded that photosystem II herbicides, bicarbonate and formate interact with each other in their binding to the Qв-protein and their interference with photosynthetic electron transport.

Effect of adrenomedullin on the production of endothelin-1 and on its vasoconstrictor action in resistance arteries: evidence for a receptor-specific functional interaction in patients with heart failure

2001 ◽  
Vol 101 (1) ◽  
pp. 45-51 ◽  
Author(s):  
Chris HILLIER ◽  
Mark C. PETRIE ◽  
Michael P. LOVE ◽  
Fiona JOHNSTON ◽  
Margaret R. MACLEAN ◽  
...  
Keyword(s):  
Heart Failure ◽  
Hill Coefficient ◽  
Receptor Interaction ◽  
Resistance Arteries ◽  
Functional Interaction ◽  
High Potassium ◽  
Endothelin 1 ◽  
Patients With Heart Failure ◽  
Small Resistance ◽  
The Hill

Endothelin-1 (ET-1) and adrenomedullin (ADM) are both produced in the arterial wall, but have opposing biological actions. Evidence from experimental animals suggests a functional interaction between ET-1 and ADM. We have tested this in humans. Small resistance arteries were obtained from gluteal biopsies taken from patients with chronic heart failure (CHF) due to coronary heart disease (CHD), or with CHD and preserved ventricular function. The contractile responses to big ET-1 and to ET-1 in both sets of vessels were studied in the absence (control) and presence of ADM at 20 pmol/l (low ADM) or 200 pmol/l (high ADM), using wire myography. ADM did not affect the conversion of big ET-1 into ET-1 in vessels from patients with either CHD or CHF. Low ADM did not alter the contractile response to ET-1 in vessels from patients with CHF. Low ADM was not tested in vessels from patients with CHD, but high ADM did not affect this response in arteries from these patients. High ADM did, however, significantly reduce the vasoconstrictor effect of ET-1 in vessels from patients with CHF. The maximum response, as a percentage of the response to high potassium, was 199% (S.E.M. 25%) in the control experiments (n = 14), 205% (27%) in the low-ADM (n = 7) studies and 150% (17%) in the high-ADM (n = 6) experiments (P < 0.001). Furthermore, the Hill coefficient increased from 0.57±0.05 in the absence of ADM to 1.16±0.15 in the high-ADM experiments, indicating that ADM at 200 pmol/l specifically antagonized one receptor type in vessels from patients with CHF. We conclude that there is a one-site receptor interaction between ADM and ET-1 that is specific for vessels from patients with CHF. This functional interaction between ADM and ET-1 in resistance arteries may be of pathophysiological importance in CHF.

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