scholarly journals Singlet oxygen damages the function of Photosystem II in isolated thylakoids and in the green alga Chlorella sorokiniana

2021 ◽  
Author(s):  
Faiza Bashir ◽  
Ateeq Ur Rehman ◽  
Milán Szabó ◽  
Imre Vass
Keyword(s):  
Photosystem Ii ◽  
Singlet Oxygen ◽  
Screening Method ◽  
Physiological Role ◽  
Thylakoid Membranes ◽  
Chlorella Sorokiniana ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Intact Cells ◽  
Green Alga Chlorella

AbstractSinglet oxygen (1O2) is an important damaging agent, which is produced during illumination by the interaction of the triplet excited state pigment molecules with molecular oxygen. In cells of photosynthetic organisms 1O2 is formed primarily in chlorophyll containing complexes, and damages pigments, lipids, proteins and other cellular constituents in their environment. A useful approach to study the physiological role of 1O2 is the utilization of external photosensitizers. In the present study, we employed a multiwell plate-based screening method in combination with chlorophyll fluorescence imaging to characterize the effect of externally produced 1O2 on the photosynthetic activity of isolated thylakoid membranes and intact Chlorella sorokiniana cells. The results show that the external 1O2 produced by the photosensitization reactions of Rose Bengal damages Photosystem II both in isolated thylakoid membranes and in intact cells in a concentration dependent manner indicating that 1O2 plays a significant role in photodamage of Photosystem II.

Inhibitory Effect of Crown Compound on Photoelectron Transport Activity of Beet Spinach Thylakoid Membranes

1991 ◽  
Vol 46 (1-2) ◽  
pp. 87-92 ◽  
Author(s):  
S. C. Sabat ◽  
V. Vijayavergiya ◽  
B. C. Tripathy ◽  
Prasanna Mohanty
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Chlorophyll A ◽  
Chlorophyll A Fluorescence ◽  
Thylakoid Membranes ◽  
Dependent Manner ◽  
Transport Activity ◽  
Concentration Dependent Manner ◽  
Variable Yield ◽  
Spinach Thylakoid

Abstract The effect of K-picrate-18-crown-6 (crown) on the photoelectron transport activity of beet spinach thylakoid membranes was investigated. Addition of micromolar concentration of crown to thylakoid preparation inhibited p-benzoquinone, chloride-indophenol, methyl viologen supported Hill activities maximally by 75 per cent in a concentration dependent manner. However, the photosystem I catalyzed reaction remained insensitive to crown suggesting that crown specifically inhibits photosystem II electron transport. Addition of exogenous electron donors like hydroxylamine or diphenylcarbazide failed to restore the crown induced inhibition of photosystem II electron transport and lowering of steady state chlorophyll a fluorescence yield. These observations suggest that crown also inhibits photosystem II catalyzed electron transport after the donation sites of these exogenous donors. Washing of the crown pre-treated thylakoids with isolation buffer, relieved the crown inhibited electron transport activity, indicating that this inhibition is reversible. Furthermore, in hydroxylamine washed thylakoids which are devoid of O2 evolution capacity, the hydroxylamine induced increase in chlorophyll a fluorescence of variable yield was quenched by the addition of crown. These observations suggest that crown affects the oxygen evolution and inhibits at a site close to photosystem II reaction centres.

scholarly journals Calcium-sensitivity of inositol 1,4,5-trisphosphate metabolism in exocrine cells from the avian salt gland

1992 ◽  
Vol 282 (3) ◽  
pp. 703-710 ◽  
Author(s):  
J P Hildebrandt ◽  
T J Shuttleworth
Keyword(s):  
Substrate Concentration ◽  
Inositol Phosphates ◽  
Receptor Activation ◽  
Dependent Manner ◽  
Salt Glands ◽  
Concentration Dependent Manner ◽  
Intact Cells ◽  
Exocrine Cells ◽  
Tissue Homogenates

The generation of inositol phosphates upon muscarinic-receptor activation was studied in [3H]inositol-loaded exocrine cells from the nasal salt glands of the duck Anas platyrhynchos, and the metabolism of different inositol phosphates in vitro was studied in tissue homogenates, with particular reference to the possible interaction of changes in intracellular [Ca2+] ([Ca2+]i) with the metabolic processes. In intact cells, there was a rapid (within 15 s) generation of Ins(1,4,5)P3 and Ins(1,3,4,5)P4, followed by an accumulation of their breakdown products, Ins(1,3,4)P3 and inositol bis- and monophosphates. Ca(2+)-sensitivity of the Ins(1,4,5)P3 3-kinase was demonstrated in tissue homogenates, with the rate of phosphorylation increasing 2-fold at free Ca2+ concentrations greater than 1 microM. However, addition of calmodulin or the presence of the calmodulin inhibitor W-7 (up to 100 microM) had no effect. 3-Kinase activity increased proportionally with the initial Ins(1,4,5)P3 concentration up to 1 microM, but a 10-fold higher substrate concentration produced only a doubling in the phosphorylation rate. Ins(1,3,4,5)P4 was dephosphorylated to Ins(1,3,4)P3, which accumulated in the homogenate assays as well as in intact cells. Depending on its concentration, Ins(1,3,4)P3 was phosphorylated [in part to Ins(1,3,4,6)P4] or dephosphorylated. To investigate the Ca(2+)-sensitivity of the 3-kinase in intact cells, excess quin2 was used to buffer the receptor-mediated transient changes in [Ca2+]i in [3H]inositol-loaded cells. These experiments revealed that increasing [Ca2+]i from less than 100 to approx. 400 nM (i.e. within the physiological range) has no effect on the partitioning of Ins(1,4,5)P3 metabolism (phosphorylation versus dephosphorylation) and on the accumulation of Ins(1,4,5)P3 and Ins(1,3,4,5)P4. This indicates that activation of the 3-kinase by physiologically relevant Ca2+ concentrations may not play a major role in the generation of Ins(1,3,4,5)P4 signals upon receptor activation in these cells. The latter are mainly achieved by the receptor-mediated increase in Ins(1,4,5)P3 in the cell and its phosphorylation by the 3-kinase in a substrate-concentration-dependent manner.

Copper Ion Inhibition of Electron Transport Activity in Sodium Chloride Washed Photosystem II Particle Is Partially Prevented by Calcium Ion

1996 ◽  
Vol 51 (3-4) ◽  
pp. 179-184 ◽  
Author(s):  
Surendra Chandra Sabat
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Calcium Ion ◽  
Electron Flow ◽  
Copper Ion ◽  
Dependent Manner ◽  
Transport Activity ◽  
Concentration Dependent Manner ◽  
Control Activity ◽  
Electron Transport Activity

Abstract The inhibitory effects of copper ion (Cu2+) on the photosynthetic electron transport func­tion was investigated both in NaCl washed (depleted in 17 and 23 kDa polypeptides) and native (unwashed) photosystem II membrane preparations from spinach (Beta vulgaris) chlo-roplasts. Copper in the range of 2.0 to 15 μᴍ strongly inhibited the electron flow from water to 2,6-dichlorobenzoquinone in NaCl washed particles in a concentration dependent manner. Com plete inhibition was noticed at 15 μᴍ Cu2+. Oppositely in native membranes, 15 μᴍ C u2+ inhibited only 10-12% of control activity. It was found that calcium ion (Ca2+) significantly reduced the Cu2+ inhibition of electron transport activity. The Ca2+ supported prevention of Cu2+ toxicity was specific to Ca2+. Further analysis indicated that both Cu2+ and Ca2+ act competitively. Since Ca2+ is known to have stimulating/stabilizing effect at the donor side of photosystem II, it is therefore suggested that Cu2+ in NaCl washed particles exerts its inhibi­tory effect(s) at the oxidizing side of photosystem stimulates/stabilizes the oxygen evolution.

Phagocytosis of platelet microvesicles and β2– glycoprotein I

2010 ◽  
Vol 104 (08) ◽  
pp. 335-341 ◽  
Author(s):  
Anhquyen Le ◽  
Anthony Prakasam ◽  
Hanan Abdel-Monem ◽  
Swapan Dasgupta ◽  
Perumal Thiagarajan
Keyword(s):  
Antiphospholipid Syndrome ◽  
Antiphospholipid Antibodies ◽  
Binding Capacity ◽  
Plasma Concentrations ◽  
Physiological Role ◽  
Maximal Effect ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Phospholipid Binding ◽  
Glycoprotein I

SummaryThe majority of the antiphospholipid antibodies, present in patients with antiphospholipid syndrome, are directed against conformational epitopes in β2-glycoprotein I. β2-glycoprotein I is an anionic phospholipid- binding 50-kDa plasma protein whose physiological role is not clear. Here we investigate the role of β2-glycoprotein I in the phagocytosis of phosphatidylserine-expressing platelet microvesicles and the effect of autoantibodies to β2-glycoprotein I on this process. We labelled the glycans of β2-glycoprotein I with BODIPY (4,4-difluoro- 4-bora-3a,4a-diaza-s-indacene)-hydrazide without affecting its phospholipid binding capacity. BODIPY-β2-glycoprotein I bound to platelet microvesicles in a concentration-dependent manner and promoted the phagocytosis of platelet microvesicles by THP-1 derived macrophages in vitro at physiological plasma concentrations with a half maximal effect at ∼10 μg/ml. β2-glycoprotein I-stimulated phagocytosis was inhibited by annexin A5 and the phosphatidylserine-binding C1C2 fragment of lactadherin. Furthermore, immunoaffinity purified β2-glycoprotein I-dependent antiphospholipid antibodies from five patients with antiphospholipid syndrome inhibited the phagocytosis in a concentration- dependent manner. These studies suggest that the binding of β2-glycoprotein I to phosphatidylserine-expressing procoagulant platelet microvesicles may promote their clearance by phagocytosis and autoantibodies to β2-glycoprotein I may inhibit this process to induce a procoagulant state.

Functional properties of noradrenergic nervous system in rat colonic mucosa: uptake of [3H]norepinephrine

1981 ◽  
Vol 241 (2) ◽  
pp. G137-G142
Author(s):  
Z. C. Wu ◽  
T. S. Gaginella
Keyword(s):  
Colonic Mucosa ◽  
Close Association ◽  
Physiological Role ◽  
Dependent Manner ◽  
Noradrenergic Neurons ◽  
Concentration Dependent Manner ◽  
Colonic Epithelial Cells ◽  
High Affinity ◽  
Maximum Inhibition ◽  
6 Hydroxydopamine

The accumulation of exogenous [3H]norepinephrine ([3H]NE) by rat colonic mucosa was studied. Uptake was linear for 10 min and reached a maximum after 90 min. The process was concentration dependent and saturable, having a Km of 1.67 X 10(-6) M and Vmax of 0.57 nmol.g-1.min-1. The inhibitor of specific norepinephrine uptake, desmethylimipramine (DMI), inhibited uptake in a concentration-dependent manner; the maximum inhibition was 81% at 10 microM. Normetanephrine also inhibited uptake at 100 microM. Reserpine, at concentrations ranging from 10(-7) to 10(-5) M, prevented the accumulation of [3H]NE, with maximum inhibition being 47% of control. Accumulation by mucosa obtained from rats sympathectomized with 6-hydroxydopamine was only 33% of control; DMI did not further reduce this uptake. Colonic epithelial cells were isolated and were found to also accumulate [3H]NE, but this accumulation was not affected by DMI. It is concluded that rat colonic mucosa contains noradrenergic neurons capable of accumulating exogenously administered norepinephrine by a specific and high-affinity process. The presence of a functional noradrenergic neural network in close association with the epithelium suggests that this system may play a physiological role in modulating colonic mucosal function.

Stimulatory effect of bradykinin on insulin release from the perfused rat pancreas

1995 ◽  
Vol 268 (5) ◽  
pp. E1027-E1030
Author(s):  
C. Yang ◽  
W. H. Hsu
Keyword(s):  
Receptor Antagonist ◽  
Insulin Release ◽  
Glucose Concentration ◽  
Physiological Role ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Perfused Rat Pancreas ◽  
Pancreas Perfusion ◽  
Rat Pancreas ◽  
Hoe 140

Rat pancreas perfusion was performed to study the effect of bradykinin on insulin release. At the perfusate glucose concentration of 6 mM, bradykinin (0.01-1 microM) increased insulin release in a concentration-dependent manner. In addition, bradykinin (1 microM) increased the glucose (10 mM)-induced insulin release. HOE-140 (0.1 microM), a bradykinin B2-receptor antagonist, decreased the baseline insulin release and abolished the bradykinin (1 microM)-induced increase in insulin release. In addition, HOE-140 (0.1 microM) attenuated the glucose (10 mM)-induced increase in insulin release. Because the blockade of bradykinin receptors by HOE-140 attenuated the glucose-induced increased insulin release, our present findings suggest that bradykinin may play a physiological role in the regulation of insulin release.

scholarly journals A5, a New Small-Molecule Inhibitor of CD4 D1 Obtained from a Computer-Aided Screening Method, Contributes to the Inhibition of CD4+ T-cell Function

2007 ◽  
Vol 12 (6) ◽  
pp. 800-808 ◽  
Author(s):  
He Xiao ◽  
Jian-Nan Feng ◽  
Zu-Yin Yu ◽  
Lei Zhang ◽  
Ming Yu ◽  
...  
Keyword(s):  
T Cell ◽  
Small Molecule ◽  
Mononuclear Cells ◽  
Cell Function ◽  
Screening Method ◽  
Interleukin 2 ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Peripheral Blood Mononuclear ◽  
Molecule Inhibitor

In this study, the authors apply a computer-based strategy to screen thousands of small-molecule, nonpeptidic organic compounds in the Available Chemicals Directory database and to select a series of potential candidates as ligands of the proposed CD4 D1 surface pocket. Then, several cell-based models are used to determine the actual biological functions of these compounds. A small molecule designated A5 ( N-((pyridine-4-yl)methylene)thiophene-2-carbohydrazide) was obtained by a virtual screening followed by 3 cell-based functional assays. The results show that A5 could specifically block the CD4—major histocompatibility complex II binding in a rosetting assay, inhibit the mixed lymphocyte reaction—induced T-cell proliferation in a concentration-dependent manner, and reduce the PMA plus ionomycin—stimulated interleukin-2 secretion from peripheral blood mononuclear cells. ( Journal of Biomolecular Screening 2007:800-808)

scholarly journals Methylamine decreases trafficking and packaging of newly synthesized phosphatidylcholine in lamellar bodies in alveolar type II cells

1996 ◽  
Vol 318 (1) ◽  
pp. 271-278 ◽  
Author(s):  
Avinash CHANDER ◽  
Namita SEN ◽  
Ai-Min WU ◽  
Stephen HIGGINS ◽  
Sandra WADSWORTH ◽  
...  
Keyword(s):  
Lung Surfactant ◽  
Brefeldin A ◽  
Alveolar Type ◽  
Type Ii Cells ◽  
Dependent Manner ◽  
Type Ii ◽  
Lamellar Bodies ◽  
Concentration Dependent Manner ◽  
Intact Cells ◽  
Isolated Lung

Lung lamellar bodies, the storage organelles for lung surfactant phosphatidylcholine (PC), maintain an acidic pH that can be increased with weak bases. This study investigates the effect of a weak base, methylamine, on the pH in lamellar bodies and on the trafficking and packaging of newly synthesized PC in lamellar bodies. Methylamine increased the pH of isolated lung lamellar bodies and of lamellar bodies in intact cells. Metabolic labelling of isolated type II cells with [methyl-3H]choline showed that although methylamine (2.5–10 mM) did not alter the labelling of cellular or microsomal PC and disaturated PC, it decreased the labelling of the PC and disaturated PC in lamellar bodies. The packaging of PC in lamellar bodies (the specific activities ratio between the PC in lamellar bodies and the microsomal PC) also decreased in a time- and concentration-dependent manner. The cellular synthesis of PC or its packaging into lamellar bodies was unaltered by brefeldin A, suggesting that the Golgi was not involved in PC packaging. Although methylamine also increased surfactant secretion, the inhibition of PC packaging in lamellar bodies seems unrelated to the secretagogue effect, (1) on the basis of metabolic consequences of increased secretion and (2) because ATP, another secretagogue, did not inhibit PC packaging. Methylamine seems to inhibit PC packaging by inhibiting trafficking of PC to lipid-rich light subcellular fractions. Together our results suggest that the trafficking of surfactant PC into lamellar bodies might be sensitive to changes in the pH of lamellar bodies.

scholarly journals N-hydroxylamine is not an intermediate in the conversion of l-arginine to an activator of soluble guanylate cyclase in neuroblastoma N1E-115 cells

1991 ◽  
Vol 273 (3) ◽  
pp. 547-552 ◽  
Author(s):  
S Pou ◽  
W S Pou ◽  
G M Rosen ◽  
E E el-Fakahany
Keyword(s):  
Guanylate Cyclase ◽  
Cyclic Gmp ◽  
Soluble Guanylate Cyclase ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Intact Cells ◽  
Relaxing Factor ◽  
Endothelium Derived Relaxing Factor ◽  
Dose Dependent

This study evaluates the role of N-hydroxylamine (NH2OH) in activating soluble guanylate cyclase in the mouse neuroblastoma clone N1E-115. It has been proposed that NH2OH is a putative intermediate in the biochemical pathway for the generation of nitric oxide (NO)/endothelium-derived relaxing factor (EDRF) from L-arginine. NH2OH caused a time- and concentration-dependent increase in cyclic GMP formation in intact cells. This response was not dependent on Ca2+. In cytosol preparations the activation of guanylate cyclase by L-arginine was dose-dependent and required Ca2+ and NADPH. In contrast, NH2OH itself did not activate cytosolic guanylate cyclase but it inhibited the basal activity of this enzyme in a concentration-dependent manner. The formation of cyclic GMP in the cytosolic fractions in response to NH2OH required the addition of catalase and H2O2. On the other hand, catalase and/or H2O2 lead to a decrease in L-arginine-induced cyclic GMP formation. Furthermore, NH2OH inhibited L-arginine- and sodium nitroprusside-induced cyclic GMP formation in the cytosol. The inhibition of L-arginine-induced cyclic GMP formation in the cytosol by NH2OH was not reversed by the addition of superoxide dismutase. These data strongly suggest that NH2OH is not a putative intermediate in the metabolism of L-arginine to an activator of guanylate cyclase.

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