Assimilatory Sulfate Reduction by Chloroplasts: The Regulatory Influence of Adenosine-mono-and Adenosine-diphosphate

Abstract The first three enzymatic steps of assimilatory sulfate reduction in chloroplasts of higher plants have been investigated with emphasis on the influence of adenosine-mono-and -diphosphate upon the formation of APS, PAPS and bound sulfite.The data show that the activation process is governed by the energy charge of the chloroplast. The regulatory step is localized at the ATP-sulfurylase reaction. It was found that this enzyme is inhibited by low concentrations of AMP and ADP, with apparent KiAMP = L8mм and KiADP=0.5 mм for the chloroplast preparations. The isolated purified ATP-sulfurylase is inhibited by the nucleotides accordingly, with KiAMP=0.2mм and KiADP=0.4mм. The results are interpreted as a regulatory mechanism for the complete process of assimilatory sulfate reduction in the chloro plast.

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Recent Results on the Assimilatory Sulfate Reduction: APS-Kinase and the Reduction of APS to Cysteine in Higher Plants

Proceedings in Life Sciences - Biology of Inorganic Nitrogen and Sulfur ◽

10.1007/978-3-642-67919-3_29 ◽

1981 ◽

pp. 334-340 ◽

Cited By ~ 6

Author(s):

J. D. Schwenn ◽

H. Urlaub

Keyword(s):

Sulfate Reduction ◽

Higher Plants ◽

Aps Kinase ◽

Assimilatory Sulfate Reduction

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Inhibition of collagen-induced platelet activation by 5'-p- fluorosulfonylbenzoyl adenosine: evidence for an adenosine diphosphate requirement and synergistic influence of prostaglandin endoperoxides

Blood ◽

10.1182/blood.v68.2.565.565 ◽

1986 ◽

Vol 68 (2) ◽

pp. 565-570 ◽

Cited By ~ 16

Author(s):

RW Colman ◽

WR Figures ◽

LM Scearce ◽

AM Strimpler ◽

FX Zhou ◽

...

Keyword(s):

Platelet Activation ◽

Shape Change ◽

Thromboxane A2 ◽

Adenosine Diphosphate ◽

Platelet Surface ◽

Prostaglandin Endoperoxide ◽

Fibrinogen Binding ◽

Low Concentrations ◽

Absolute Requirement

Abstract The relative roles of platelet autacoids such as adenosine diphosphate (ADP), prostaglandin endoperoxides, and thromboxane A2 (TXA2) in collagen-induced platelet activation are not fully understood. We reexamined this relationship using the ADP affinity analogue, 5'-p- fluorosulfonylbenzoyl adenosine (FSBA), which covalently modifies a receptor for ADP on the platelet surface, thereby inhibiting ADP- induced platelet activation. Collagen-induced shape change, aggregation, and fibrinogen binding were each fully inhibited under conditions in which FSBA is covalently incorporated and could not be overcome by raising the collagen used to supramaximal concentrations. In contrast, TXA2 synthesis stimulated by collagen under conditions that produced maximum aggregation was only minimally inhibited by FSBA. Since covalent incorporation of FSBA has been previously shown to specifically inhibit ADP-induced activation of platelets, the present study supports the contention that ADP is required for collagen-induced platelet activation. Under similar conditions, indomethacin, an inhibitor of cyclooxygenase, inhibited collagen-induced shape change, indicating that endoperoxides and/or TXA2 also play a role in this response. Shape change induced by low concentrations (10 nmol/L) of the stable prostaglandin endoperoxide, azo-PGH2, was also inhibited by FSBA. These observations indicate a role for ADP in responses elicited by low concentrations of endoperoxides. However, at higher concentrations of azo-PGH2 (100 nmol/L), inhibition by FSBA could be overcome. Thus, the effect of collagen apparently has an absolute requirement for ADP for aggregation and fibrinogen binding and for both ADP and prostaglandins for shape change. Aggregation and fibrinogen binding induced by prostaglandin endoperoxides also required ADP as a mediator, but ADP is not absolutely required at high endoperoxide concentration to induce shape change.

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Platelet functions and energy metabolism in a patient with hexokinase deficiency

Blood ◽

10.1182/blood.v63.1.147.147 ◽

1984 ◽

Vol 63 (1) ◽

pp. 147-153 ◽

Cited By ~ 9

Author(s):

JW Akkerman ◽

G Rijksen ◽

G Gorter ◽

GE Staal

Keyword(s):

Adenine Nucleotides ◽

Energy Charge ◽

Energy Generation ◽

Adenosine Diphosphate ◽

Dense Granule ◽

Glycolytic Flux ◽

Adenylate Energy Charge ◽

Severe Reduction ◽

Dense Granule Secretion ◽

Granule Secretion

Abstract We have studied the regeneration of adenosine triphosphate (ATP) in the glycolytic pathway in platelets with a 75% reduction in hexokinase (HK) activity and have investigated aggregation and Ca2+ secretion. HK- deficient platelets had a normal glycolytic flux in the resting state, but responded insufficiently to stimulation with thrombin (5 U/ml). In contrast, glycogen contents and glycogenolysis were normal. When the metabolic adenine nucleotides were labeled with 14C-adenine, the patient's platelets showed a normal adenylate energy charge and a normal level of 14C-ATP. However, the inhibitor of mitochondrial energy generation, CN-, induced a weaker fall in 14C-ATP in the patient's platelets than in the controls. Analysis of secretion markers revealed decreased amounts of granule-bound ATP and secretable Ca2+, whereas granule-bound adenosine diphosphate (ADP), beta-thromboglobulin, N- acetyl-beta-D-glucosaminidase, and beta-glucuronidase were within the normal range. Aggregation and Ca2+ secretion induced by 5 U/ml thrombin were normal and were not changed in the presence of inhibitors of mitochondrial and glycogenolytic energy generation. Aggregation was also normal at 0.1 U/ml thrombin and was independent of these inhibitors, but Ca2+ secretion was greatly impaired when mitochondrial and glycogenolytic ATP resynthesis was abolished. These findings indicate that a severe reduction in HK activity causes insufficient acceleration of the glycolytic flux during stimulation with thrombin. This leads to impaired dense granule secretion in conditions where secretion depends on concurrent ATP resynthesis and glycolysis is rate limiting.

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Ticlopidine Selectively Inhibits Human Platelet Responses to Adenosine Diphosphate

Thrombosis and Haemostasis ◽

10.1055/s-0038-1646487 ◽

1991 ◽

Vol 66 (06) ◽

pp. 694-699 ◽

Cited By ~ 49

Author(s):

Marco Cattaneo ◽

Benjaporn Akkawat ◽

Anna Lecchi ◽

Claudio Cimminiello ◽

Anna M Capitanio ◽

...

Keyword(s):

Platelet Aggregation ◽

Adenosine Diphosphate ◽

Inhibitory Effect ◽

Clot Retraction ◽

Fibrinogen Binding ◽

Low Concentrations ◽

Binding Inhibition ◽

High Concentrations ◽

Formalin Fixed

SummaryPlatelet aggregation and fibrinogen binding were studied in 15 individuals before and 7 days after the oral administration of ticlopidine (250 mg b.i.d.). Ticlopidine significantly inhibited platelet aggregation induced by adenosine diphosphate (ADP), the endoperoxide analogue U46619, collagen or low concentrations of thrombin, but did not inhibit platelet aggregation induced by epinephrine or high concentrations of thrombin. Ticlopidine inhibited 125I-fibrinogen binding induced by ADP, U46619 or thrombin (1 U/ml). The ADP scavengers apyrase or CP/CPK, added in vitro to platelet suspensions obtained before ticlopidine, caused the same pattern of aggregation and 125I-fibrihogen binding inhibition as did ticlopidine. Ticlopidine did not inhibit further platelet aggregation and 125I-fibrinogen binding induced in the presence of ADP scavengers. After ticlopidine administration, thrombin or U46619, but not ADP, increased the binding rate of the anti-GPIIb/IIIa monoclonal antibody 7E3 to platelets. Ticlopidine inhibited clot retraction induced by reptilase plus ADP, but not that induced by thrombin or by reptilase plus epinephrine, and prevented the inhibitory effect of ADP, but not that of epinephrine, on the PGE1-induced increase in platelet cyclic AMP. The number of high- and low-affinity binding sites for 3H-ADP on formalin-fixed platelets and their K d were not modified by ticlopidine. These findings indicate that ticlopidine selectively inhibits platelet responses to ADP.

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Changes of platelets’ function in preeclampsia

Open Medicine ◽

10.2478/s11536-011-0076-3 ◽

2011 ◽

Vol 6 (6) ◽

pp. 696-700

Author(s):

Goran Babic ◽

Slobodan Novokmet ◽

Slobodan Jankovic

Keyword(s):

Platelet Aggregation ◽

Adenine Nucleotides ◽

Energy Charge ◽

Adenosine Diphosphate ◽

Control Group ◽

Adenylate Energy Charge ◽

Cross Sectional ◽

Blood Samples ◽

Metabolic Pool ◽

Aggregation Of Platelets

AbstractIncreased aggregation of platelets during preeclampsia was shown in several studies, yet several others reported no change. The aim of our study was to investigate platelet aggregation in a group of patients suffering from preeclampsia. In a cross-sectional study blood samples were taken from 89 hospitalized patients in the third trimester of pregnancy: 38 were suffering from mild to moderate preeclampsia and 51 patients were without preeclampsia. From the blood samples platelet aggregation, secretion of adenine nucleotides from platelets, concentration of energy-rich adenine compounds and levels of cyclic adenosine-mono-phosphate and cyclic guanosine mono-phosphate in platelets were measured. In the patients with preeclampsia, the adenosine diphosphate threshold for biphasic aggregation [odds ratio (OR):.75; 95% Confidence Interval (CI): 0.55–1.02; p<0.05], total adenine nucleotides concentration in the metabolic pool of platelets (OR:0.99; CI: 0.62–1.57; p<0.01) and cyclic adenosine-mono-phosphate (OR:0.81; CI: 0.57, 1.14; p<0.05) and cyclic guanosine mono-phosphate (OR:.78; CI: 0.55–1.09; p<0.05) levels in platelets were decreased in comparison with the control group, while adenylate energy charge in the metabolic pool of platelets (OR: >100.00; CI: 0.00->100.00; p<0.05) and secretion of adenosine triphosphate (OR:.13; CI: 0.00–14.26; p<0.05) and adenosine diphosphate (OR:.77; CI: 0.08–36.79; p<0.05) were increased. The results of our study show increased activation and aggregation of platelets in pregnant females with preeclampsia.

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A Key Role of Adenosine Diphosphate in the Irreversible Platelet Aggregation Induced by the PAR1-Activating Peptide Through the Late Activation of Phosphoinositide 3-Kinase

Blood ◽

10.1182/blood.v94.12.4156 ◽

1999 ◽

Vol 94 (12) ◽

pp. 4156-4165 ◽

Cited By ~ 165

Author(s):

Catherine Trumel ◽

Bernard Payrastre ◽

Monique Plantavid ◽

Béatrice Hechler ◽

Cécile Viala ◽

...

Keyword(s):

Platelet Activation ◽

Kinase Inhibitors ◽

Adenosine Diphosphate ◽

Blood Platelet ◽

Activation Process ◽

Irreversible Aggregation ◽

Stable Association ◽

Phosphoinositide 3 Kinase

Abstract Although adenosine diphosphate (ADP), per se, is a weak platelet agonist, its role as a crucial cofactor in human blood platelet functions has now been clearly demonstrated in vitro and in vivo. The molecular basis of the ADP-induced platelet activation is starting to be understood since the discovery that 2 separate P2 purinergic receptors may be involved simultaneously in the activation process. However, little is known about how ADP plays its role as a cofactor in platelet activation and which signaling pathway initiated by a specific agonist can be modulated by the released ADP. To investigate these points, we took advantage of a model of platelet activation through the thrombin receptor PAR1 in which both ADP scavengers and phosphoinositide 3-kinase (PI 3-kinase) inhibitors have been shown to transform the classical irreversible aggregation into a reversible one. We have observed that, among the different PI 3-kinase products, the accumulation of phosphatidylinositol 3,4-bisphosphate [PtdIns(3,4)P2] was dramatically and specifically attenuated when ADP was removed by apyrase treatment. A comparison between the effects of PI 3-kinase inhibitors and apyrase strongly suggest that the late, ADP-dependent, PtdIns(3,4)P2accumulation is necessary for PAR1-induced irreversible aggregation. Using selective antagonists, we found that the effect of ADP was due to the ADP receptor coupled to inhibition of adenylyl cyclase. Finally, we found that both ADP and PI 3-kinase play an important role in PAR1-dependent reorganization of the cytoskeleton through a control of myosin heavy chain translocation and the stable association of signaling complexes with the actin cytoskeleton.

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