scholarly journals Quantitative determination of the binding of β2-glycoprotein I and prothrombin to phosphatidylserine-exposing blood platelets

2005 ◽  
Vol 386 (2) ◽  
pp. 271-279 ◽  
Author(s):  
Edouard M. BEVERS ◽  
Marie P. JANSSEN ◽  
Paul COMFURIUS ◽  
Krishnakumar BALASUBRAMANIAN ◽  
Alan J. SCHROIT ◽  
...  
Keyword(s):  
Ionic Strength ◽  
Binding Sites ◽  
Blood Platelets ◽  
Lipid Binding ◽  
Ellipsometric Measurement ◽  
Glycoprotein I ◽  
Kd Values ◽  
Low Ionic Strength ◽  
Lipid Binding Proteins

The plasma protein β2GPI (β2-glycoprotein I) has been proposed to mediate phagocytosis of apoptotic cells and to play a role in the antiphospholipid syndrome. This suggestion is based mainly on the presumption that β2GPI has an appreciable interaction with PS (phosphatidylserine)-exposing cell membranes. However, quantitative data on the binding of β2GPI to PS-exposing cells under physiologically relevant conditions are scarce and conflicting. Therefore we evaluated the binding of β2GPI to PS-expressing blood platelets. Flow cytometry showed that binding of β2GPI is negligible at physiological ionic strength, in contrast with significant binding occurring at low ionic strength. Binding parameters of β2GPI and (for comparison) prothrombin were quantified by ellipsometric measurement of protein depletion from the supernatant following incubation with platelets. At low ionic strength (20 mM NaCl, no CaCl2), a dissociation constant (Kd) of 0.2 μM was found for β2GPI, with 7.4×105 binding sites per platelet. Under physiologically relevant conditions (120 mM NaCl and 3 mM CaCl2), binding of β2GPI was not detectable (extrapolated Kd>80 μM). Prothrombin binding (at 3 mM CaCl2) was much less affected by ionic strength: Kd values of 0.5 and 1.4 μM were observed at 20 and 120 mM NaCl respectively. The low affinity and the presence of many lipid-binding proteins in plasma that can compete with the binding of β2GPI suggest that only a small fraction (<5%) of the binding sites on PS-exposing blood cells are likely to be occupied by β2GPI. These findings are discussed in relation to the alleged (patho-)physiological functions of β2GPI.

Interaction of β2-Glycoprotein-I with Human Blood Platelets: Influence Upon the ADP-Induced Aggregation

1985 ◽  
Vol 54 (02) ◽  
pp. 397-401 ◽  
Author(s):  
Johannes Nimpf ◽  
Helmut Wurm ◽  
Gerhard M Kostner
Keyword(s):  
Binding Sites ◽  
Specific Binding ◽  
Blood Platelets ◽  
Gel Filtration ◽  
Human Platelets ◽  
Glycoprotein I ◽  
Unspecific Binding ◽  
Induced Aggregation ◽  
Human Blood Platelets

SummaryThe interaction of β2-glycoprotein-I (β2-G-I), a plasma constituent of unknown function, with blood platelets was studied. The following results were obtained: 1) β2-G-I binds to washed human platelets isolated by centrifugation (WP) at one kind of specific, saturable binding sites. The dissociation constant was found to be approx. 1 × 10−6M.2) In the presence of physiological concentrations of Ca++ (2.5 mM), this specific binding is markedly reduced. Unspecific binding of β2-G-I to platelets, however, is not influenced by Ca++.3) Platelets prepared by gel filtration (GFP), differing in their in vitro aggregability from WP, exhibit no specific binding of β2-G-I. Binding to GFP is also not induced by activation with thrombin, collagen or ADP.4) β2-G-I causes significant alteration of the ADP-induced aggregation of GFP. Aggregation induced by thrombin, collagen, arachidonic acid or PAF-acether, however is not altered by β2G-I.It is suggested, that pelleting during centrifugation causes irreversible rearrangements in the membrane of platelets.

scholarly journals Use of an ion-selective electrode for free copper measurements in low salinity and low ionic strength matrices

2007 ◽  
Vol 4 (2) ◽  
pp. 90 ◽  
Author(s):  
Julien Rachou ◽  
Christian Gagnon ◽  
Sébastien Sauvé
Keyword(s):  
Ionic Strength ◽  
Ion Selective Electrode ◽  
Metal Species ◽  
Analytical Determination ◽  
Operational Parameters ◽  
Selective Electrode ◽  
Time Saving ◽  
Low Salinity ◽  
Low Ionic Strength

Environmental context. The toxicity of metals in the environment is controlled by several parameters including total metal concentration, pH and organic and inorganic ligands (type and concentration). The characterisation of different metal pools in natural matrices (e.g. seawater, soil) is important for the evaluation of their toxic impact. The copper ion-selective electrode (Cu-ISE) is a method of choice for the analytical determination of the speciation (i.e. chemical forms) of divalent copper in natural matrices. This paper clarifies several operational parameters in the hope of decreasing variability of results and increasing the application domain of the Cu-ISE. Abstract. The determination of free copper concentrations in natural matrices is critical for the evaluation of copper toxicity. The ISE is one of the few analytical means for determining the direct speciation of free metal species. We have refined the method for low salinity and low ionic strength solutions for application with soil water extracts or fresh waters. Moreover, we have detailed and standardised a method for using a Cu-ISE with an autotitrator. The standardisation shows a good response and allows significant time saving (under 2 h for the calibration). The results obtained using the ISE are compared with those predicted in the presence of different organic ligands or even the lower free Cu2+ activities resulting from the formation of Cu hydroxyl species. The method was validated for the determination of Cu speciation at environmentally relevant free Cu2+ activity, i.e. ranging between 10−14 to 10−4 M. The chemical equilibrium calculations were made using the MINEQL+ software and the results agree well for pH values between 3 and 10. In terms of precision, the standard deviations of the measured values never exceed 0.1 units, and in terms of accuracy, the measured values were very close to the nominal values, within a range of 0.1. Outside the optimal pH range, the electrode yields higher activity than expected.

Modulation Of Adenylate Cyclase Activity In Platelets By β2-Glycoprotein I

1981 ◽  
Author(s):  
Inger Schousboe
Keyword(s):  
Ionic Strength ◽  
Adenylate Cyclase ◽  
Human Serum ◽  
Human Platelets ◽  
Cyclase Activity ◽  
Adenylate Cyclase Activity ◽  
Glycoprotein I ◽  
Low Concentrations ◽  
Low Ionic Strength

β2GlycoProtein I, purified from human serum, has been shown to bind to negatively charged phospholipids. Such phospholipids axe essential reactants in several surface mediated reactions. In blood coagulation, platelets, to which β2-glycoprotein I recently has been shown to bind, furnish a major portion of these phospholipids. Concomitant with this binding, a change in platelet adenylate cyclase activity has been observed. The purpose of this study is to further investigate the effect of β2-glycoprotein I on the adenylate cyclase activity in platelets.Human platelets isolated immediately after bleeding were washed in buffered isotonic solutions at low ionic strength. At 0 °C intact or sonicated platelets were incubated with various concentrations of β2-glycoprotein I and prostaglandin E1xs. Intact platelets were then sonicated, platelet membranes isolated and frozen at -180 °C, and adenylate cyclase activity of the membranes determined.The results showed that adenylate cyclase activity in platelets increases about 4 times when intact platelets are preincubated with β2-glycoprotein I at saturation. This increase is also seen when low concentrations of PGE1 (≤ lµM) are present in the preincubation mixture. There was no increase in adenylate cyclase activity when sonicated platelets were incubated with β2-glycoprotein I.On the basis of these results it is suggested that in vivo β2-glycoprotein I may have one or both of the following functions, l) It may prevent circulating platelets from aggregation by protecting the negatively charged phospholipids and/or by increasing the adenylate cyclase activity and 2) it may catalyze the deaggregation of aggregated platelets.

Determination of electroosmotic and electrophoretic mobility of DNA and dyes in low ionic strength solutions

2017 ◽  
Vol 39 (5-6) ◽  
pp. 862-868 ◽  
Author(s):  
Joshua Lallman ◽  
Rachel Flaugh ◽  
Kristy L. Kounovsky-Shafer
Keyword(s):  
Ionic Strength ◽  
Electrophoretic Mobility ◽  
Low Ionic Strength

scholarly journals Determination of free metal ion concentrations with AGNES in low ionic strength media

2013 ◽  
Vol 689 ◽  
pp. 276-283 ◽  
Author(s):  
D. Aguilar ◽  
C. Parat ◽  
J. Galceran ◽  
E. Companys ◽  
J. Puy ◽  
...  
Keyword(s):  
Ionic Strength ◽  
Metal Ion ◽  
Ion Concentrations ◽  
Low Ionic Strength ◽  
Free Metal ◽  
Free Metal Ion

Recommendations for the determination of pH in low ionic strength fresh waters

1985 ◽  
Vol 57 (6) ◽  
pp. 877-886 ◽  
Author(s):  
A. K. Covington ◽  
P. D. Whalley ◽  
William Davison
Keyword(s):  
Ionic Strength ◽  
Fresh Waters ◽  
Low Ionic Strength

Determination of Trace Metals in Low Ionic Strength Waters Using Zeeman and Deuterium Background Correction for Graphite Furnace Atomic Absorption Spectrometry

1986 ◽  
Vol 69 (4) ◽  
pp. 704-708
Author(s):  
Marvin J Fishman ◽  
Gary R Perryman ◽  
LeRoy J Schroder ◽  
Edward W Matthews
Keyword(s):  
Ionic Strength ◽  
Graphite Furnace ◽  
Absorption Spectrometry ◽  
Sample Volume ◽  
Background Correction ◽  
Analytical Wavelength ◽  
Graphite Furnace Atomic Absorption ◽  
Low Ionic Strength ◽  
Copper Lead

Abstract Each U.S. Geological Survey water quality laboratory evaluated one of 2 background correction techniques: Zeeman and deuterium. A L’vov-type platform was used to determine cadmium, chromium, cobalt, copper, lead, manganese, nickel, and zinc in low ionic strength waters, submitted as blind samples. Matrix modifers were used to determine cadmium, chromium, lead, manganese, and zinc. Results were comparable for all metals, except cadmium and nickel, at the μg/L range. Analytical ranges for a 20 μL sample volume are presented. Detection limits can be changed by varying the volume of sample injected, by using multiple injections, or by changing the analytical wavelength.

Sign in / Sign up

Export Citation Format

Share Document