scholarly journals Heparin-stimulated inhibition of factor IXa generation and factor IXa neutralization in plasma

Blood ◽  
1990 ◽  
Vol 76 (3) ◽  
pp. 549-554 ◽  
Author(s):  
J Pieters ◽  
T Lindhout ◽  
G Willems
Keyword(s):  
Unfractionated Heparin ◽  
Rate Constant ◽  
Calcium Ions ◽  
Order Rate Constant ◽  
Free Calcium ◽  
First Order ◽  
Factor Ixa ◽  
Factor Xia ◽  
Kinetics Of

Abstract Generation and inhibition of activated factor IXa was studied in factor XIa-activated plasma containing 4 mmol/L free calcium ions and 20 mumol/L phospholipid (25 mol% phosphatidylserine/75 mol% phosphatidylcholine). Interference of other (activated) clotting factors with the factor IXa activity measurements could be avoided by using a highly specific and sensitive bioassay. Factor IXa generation curves were analyzed according to a model that assumed Michaelis-Menten kinetics of factor XIa-catalyzed factor IXa formation and pseudo first order kinetics of inhibition of factor XIa and factor IXa. In the absence of heparin, factor IXa activity in plasma reached final levels that were found to increase with increasing amounts of factor XIa used to activate the plasma. When the model was fitted to this set of factor IXa generation curves, the analysis yielded a rate constant of inhibition of factor XIa of 0.7 +/- 0.1 min-1 and a kcat/Km ratio of 0.29 +/- 0.01 (nmol/L)-1 min-1. No neutralization of factor IXa activity was observed (the estimated rate constant of inhibition of factor IXa was 0). Thus, in the absence of heparin, the final level of factor IXa in plasma is only dependent on the initial factor XIa concentration. While neutralization of in situ generated factor IXa in normal plasma was negligible, unfractionated heparin dramatically enhanced the rate of inactivation of factor IXa (apparent second order rate constant of inhibition of 5.2 min-1/per microgram heparin/mL). The synthetic pentasaccharide heparin, the smallest heparin chain capable of binding antithrombin III, stimulated the inhibition of in situ generated factor IXa, but sevenfold less than unfractionated heparin (k = 0.76 min-1 per microgram pentasaccharide/mL). We found that free calcium ions were absolutely required to observe an unfractionated heparin and pentasaccharide-stimulated neutralization of factor IXa activity. Factor XIa inhibition (psuedo first order rate constant of 0.7 min-1) was not affected by unfractionated heparin or pentasaccharide in the range of heparin concentrations studied.

scholarly journals Heparin-stimulated inhibition of factor IXa generation and factor IXa neutralization in plasma

Blood ◽  
1990 ◽  
Vol 76 (3) ◽  
pp. 549-554
Author(s):  
J Pieters ◽  
T Lindhout ◽  
G Willems
Keyword(s):  
Unfractionated Heparin ◽  
Rate Constant ◽  
Calcium Ions ◽  
Order Rate Constant ◽  
Free Calcium ◽  
First Order ◽  
Factor Ixa ◽  
Factor Xia ◽  
Kinetics Of

Generation and inhibition of activated factor IXa was studied in factor XIa-activated plasma containing 4 mmol/L free calcium ions and 20 mumol/L phospholipid (25 mol% phosphatidylserine/75 mol% phosphatidylcholine). Interference of other (activated) clotting factors with the factor IXa activity measurements could be avoided by using a highly specific and sensitive bioassay. Factor IXa generation curves were analyzed according to a model that assumed Michaelis-Menten kinetics of factor XIa-catalyzed factor IXa formation and pseudo first order kinetics of inhibition of factor XIa and factor IXa. In the absence of heparin, factor IXa activity in plasma reached final levels that were found to increase with increasing amounts of factor XIa used to activate the plasma. When the model was fitted to this set of factor IXa generation curves, the analysis yielded a rate constant of inhibition of factor XIa of 0.7 +/- 0.1 min-1 and a kcat/Km ratio of 0.29 +/- 0.01 (nmol/L)-1 min-1. No neutralization of factor IXa activity was observed (the estimated rate constant of inhibition of factor IXa was 0). Thus, in the absence of heparin, the final level of factor IXa in plasma is only dependent on the initial factor XIa concentration. While neutralization of in situ generated factor IXa in normal plasma was negligible, unfractionated heparin dramatically enhanced the rate of inactivation of factor IXa (apparent second order rate constant of inhibition of 5.2 min-1/per microgram heparin/mL). The synthetic pentasaccharide heparin, the smallest heparin chain capable of binding antithrombin III, stimulated the inhibition of in situ generated factor IXa, but sevenfold less than unfractionated heparin (k = 0.76 min-1 per microgram pentasaccharide/mL). We found that free calcium ions were absolutely required to observe an unfractionated heparin and pentasaccharide-stimulated neutralization of factor IXa activity. Factor XIa inhibition (psuedo first order rate constant of 0.7 min-1) was not affected by unfractionated heparin or pentasaccharide in the range of heparin concentrations studied.

Oxidation of Nickel(II) and Manganese(II) by Peroxodisulfate in Aqueous Solution in the Presence of Molybdate. Crystal Structure of the (NH4)6[NiMo9O32].6H2O Product

1992 ◽  
Vol 45 (12) ◽  
pp. 1943 ◽  
Author(s):  
SJ Dunne ◽  
RC Burns ◽  
GA Lawrance
Keyword(s):  
Rate Constant ◽  
Linear Dependence ◽  
Ph Dependence ◽  
Order Rate Constant ◽  
X Ray Diffraction ◽  
X Ray ◽  
First Order ◽  
Oxidant Concentration ◽  
Ph Range ◽  
Kinetics Of

Oxidation of Ni2+,aq, by S2O82- to nickel(IV) in the presence of molybdate ion, as in the analogous manganese system, involves the formation of the soluble heteropolymolybdate anion [MMogO32]2- (M = Ni, Mn ). The nickel(IV) product crystallized as (NH4)6 [NiMogO32].6H2O from the reaction mixture in the rhombohedra1 space group R3, a 15.922(1), c 12.406(1) � ; the structure was determined by X-ray diffraction methods, and refined to a residual of 0.025 for 1741 independent 'observed' reflections. The kinetics of the oxidation were examined at 80 C over the pH range 3.0-5.2; a linear dependence on [S2O82-] and a non-linear dependence on l/[H+] were observed. The influence of variation of the Ni/Mo ratio between 1:10 and 1:25 on the observed rate constant was very small at pH 4.5, a result supporting the view that the precursor exists as the known [NiMo6O24H6]4- or a close analogue in solution. The pH dependence of the observed rate constant at a fixed oxidant concentration (0.025 mol dm-3) fits dequately to the expression kobs = kH [H+]/(Ka+[H+]) where kH = 0.0013 dm3 mol-1 s-1 and Ka = 4-0x10-5. The first-order dependence on peroxodisulfate subsequently yields a second-order rate constant of 0.042 dm3 mol-1 s-1. Under analogous conditions, oxidation of manganese(II) occurs eightfold more slowly than oxidation of nickel(II), whereas oxidation of manganese(II) by peroxomonosulfuric acid is 16-fold faster than oxidation by peroxodisulfate under similar conditions.

Kinetics of reconstitution of apotyrosinase by copper

1990 ◽  
Vol 68 (2) ◽  
pp. 476-479
Author(s):  
Donald C. Wigfield ◽  
Douglas M. Goltz
Keyword(s):  
Rate Constant ◽  
Copper Concentration ◽  
Copper Ions ◽  
Copper Ion ◽  
Order Rate Constant ◽  
First Order ◽  
Order Rate ◽  
Pseudo First Order ◽  
Rate Limiting ◽  
Kinetics Of

The kinetics of the reconstitution reaction of apotyrosinase with copper (II) ions are reported. The reaction is pseudo first order with respect to apoenzyme and the values of these pseudo first order rate constants are reported as a function of copper (II) concentration. Two copper ions bind to apoenzyme, and if the second one is rate limiting, the kinetically relevant copper concentration is the copper originally added minus the amount used in binding the first copper ion to enzyme. This modified copper concentration is linearly related to the magnitude of the pseudo first order rate constant, up to a copper concentration of 1.25 × 10−4 M (10-fold excess), giving a second order rate constant of 7.67 × 102 ± 0.93 × 102 M−1∙s−1.Key words: apotyrosinase, copper, tyrosinase.

Kinetics of Reactions of 8-Quinolinol and Acetate with Hydroxyaluminum Species in Aqueous Solutions. 1. Polynuclear Hydroxyaluminum Cations

1971 ◽  
Vol 49 (10) ◽  
pp. 1683-1687 ◽  
Author(s):  
R. C. Turner ◽  
Wan Sulaiman
Keyword(s):  
Acetic Acid ◽  
Rate Constant ◽  
Empirical Equation ◽  
Decomposition Reaction ◽  
Order Rate Constant ◽  
Acetate Concentration ◽  
First Order ◽  
Order Rate ◽  
Pseudo First Order ◽  
Kinetics Of

The effect of varying 8-quinolinol and acetate concentration on the rate of decomposition of poly-nuclear hydroxyaluminum cations was studied. It was found that the concentration of the undissociated 8-quinolinol and acetic acid molecules determined the magnitude of the first order rate constant for the decomposition of the polynuclear hydroxyaluminum cations, except when the acetate concentrations were relatively high. With high acetate concentrations, it appeared that polynuclear acetate species were involved in the reactions. An empirical equation was developed showing the effect of 8-quinolinol and acetic acid molecule concentrations on the pseudo first order rate constant for the decomposition reaction.

Kinetics of Exchange of Dimethylsulfoxide between Hexakis(dimethylsulfoxide)chromium(III) and Solvent: Pressure Effect and Mechanism

1973 ◽  
Vol 51 (22) ◽  
pp. 3795-3798 ◽  
Author(s):  
Debra Lynn Carle ◽  
Thomas Wilson Swaddle
Keyword(s):  
Rate Constant ◽  
Pressure Effect ◽  
Order Rate Constant ◽  
First Order ◽  
Order Rate ◽  
Kinetics Of

For the exchange of all six dimethylsulfoxide (DMSO) ligands in Cr(DMSO)63+ with perdeuterated DMSO solvent, the first-order rate constant (75°) = 5.5 × 10−5 s−1, while ΔH* = 23.1 kcal mol−1, ΔS* = − 11.8 cal deg−1 mol−1, and ΔV* = − 11.3 cm3 mol−1. These and other data are indicative of an associative interchange mechanism for substitution in Cr(III) DMSO complexes in DMSO.

Protein Z Dependent Protease Inhibitor Inhibition of Factor XIa Is Accelerated by Unfractionated Heparin in the Presence and Absence of Protein Z: Further Evidence of the Potential Significance of XIa Inhibitory Activity.

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 2032-2032
Author(s):  
Laura Young ◽  
Neil Van de Water ◽  
Paul L Harper ◽  
Paul A. Ockelford ◽  
Anita Horvath ◽  
...  
Keyword(s):  
Protease Inhibitor ◽  
Unfractionated Heparin ◽  
Inhibitory Activity ◽  
Fold Increase ◽  
Order Rate Constant ◽  
Phospholipid Vesicles ◽  
Protein Z ◽  
First Order ◽  
Order Rate ◽  
Factor Xia

Abstract Protein Z dependent protease inhibitor (ZPI) is a human plasma serpin that inhibits factors Xa and XIa in the coagulation pathway. Kinetic studies have shown that ZPI is an efficient inhibitor of factor Xa. This interaction is accelerated by protein Z in the presence of calcium and phospholipid. The inhibition of factor XIa is by an alternative mechanism that does not require phospholipid but is influenced by both heparin and protein Z; heparin increases inhibition whereas protein Z /calcium delays inhibition. The latter maybe physiologically relevant to XIa inhibitory activity as ZPI and protein Z circulate in complex in plasma, with ZPI in slight excess. The kinetics of ZPI/XIa/heparin interactions have not been fully characterised. In this study we report the kinetic analysis of the interaction between factor XIa and recombinant ZPI expressed in Escherichia coli, in the presence of unfractionated heparin, pentasaccharide and protein Z. Results: Recombinant ZPI (rZPI) had characteristics similar to native protein as previously described; serpin-protease complexes were non-covalent, and reactive centre loop proteolytic cleavage of ZPI was noted during this reaction. On SDS gel rZPI had a molecular weight of 50kDa. Circular dichroism of rZPI showed an unfolding transition on thermal denaturation typical of a serpin in native conformation with a Tm of 58.8°C. In contrast loop cleaved rZPI had increased thermal stability as expected for a serpin. A discontinuous method was used to measure the rate of inhibition of target proteases by rZPI; the first order rate constant was measured over time under pseudo first order conditions, and was used to derive the second order rate constant (ka) as shown in Table 1. Table 1: Second order rate constants (ka) Xa (Ms−1) XIa (Ms−1) * And calcium/phospholipid vesicles ZPI 1.9 x 103 9.0 x 104 ZPI + protein Z* 6.6 x 105 1.8 x 104 ZPI + unfractionated heparin (1IU/mL) - 1.0 x 106 ZPI + pentasaccharide (500nM) - 1.0 x 105 ZPI + protein Z* + unfractionated heparin (1IU/mL) - 6.0 x 105 In the presence of calcium and phospholipid vesicles the ka for Xa in the absence and presence of protein Z was similar to previous reports. The ka for ZPI inhibition of XIa increased 11 fold in the presence of unfractionated heparin. Heparin titration curves suggest that a template mechanism is likely; the heparin pentasaccharide had no impact on inhibition rate consistent with this observation. It has previously been reported that protein Z impedes the ZPI inhibition of XIa; our results support this with a 5-fold reduction in ka. However the addition of heparin to ZPI in the presence of Protein Z leads to a significant 33-fold increase in inhibitory activity with a rate similar to the inhibitory activity of ZPI against Xa in the presence of protein Z. Conclusions: There are several physiological inhibitors of factor XIa. In previous reports ZPI inhibition only increased 2-fold in the presence of heparin. Our results confirm that heparin increases the ZPI inhibition of XIa but with a significantly higher increase than previously reported. The increase in activity is even more marked in the presence of protein Z. Although protein Z alone inhibits ZPI activity against XIa the combination with heparin achieves a 33 fold increase in activity. Of all the serpin inhibitors of XIa, antithrombin is considered a major inhibitor in the presence of heparin. Our results show that the ka for FXIa inhibition in the presence of ZPI, protein Z and heparin is more than 20 fold higher than the ka reported for the antithrombin/heparin inhibition of XIa (2-3x104Ms−1). We have previously reported a higher incidence of venous thrombosis in patients with nonsense mutations in the ZPI gene suggesting the clinical significance of this protein. The suggestion that the inhibition of XIa maybe more relevant than that of Xa has been raised in recent murine work where ZPI knockouts have a more severe phenotype than protein Z knockouts. ZPI inhibition of XIa in the presence of endogenous heparins maybe an important contributor to its physiological significance.

Kinetics of halogen substituted aniline transformation in anaerobic estuarine sediment

1996 ◽  
Vol 34 (7-8) ◽  
pp. 37-43 ◽  
Author(s):  
Sridhar Susarla ◽  
Shigeki Masunaga ◽  
Yoshitaka Yonezawa
Keyword(s):  
Rate Constant ◽  
Halogen Bond ◽  
Order Rate Constant ◽  
Quantitative Structure Activity Relationship ◽  
Estuarine Sediment ◽  
Substituted Anilines ◽  
First Order ◽  
The Relationship ◽  
Steric Constant ◽  
Kinetics Of

The kinetics of halogen substituted anilines were examined in estuarine sediment collected from Tsurumi river, Japan. Aniline was substituted with F, Cl, Br and I groups at meta or para positions on the aromatic ring. The transformation of all the compounds followed a first-order reaction kinetics with rate constants for the disappearance ranging between 0.002 to 0.006 day−1 or half lives between 108 and 669 days. Results indicated that para substituted anilines transformed two to four times faster compared to meta substituted ones. The rate of transformation followed the order: I > Br > Cl > F. A quantitative structure-activity relationship was evaluated relating the first-order rate constant in sediment with several readily available molecular descriptors: carbon-halogen bond strength, Hammett sigma constants, Taft steric constant, and Lipophilic constant. In addition octanol/water partition coefficients and solubility were included in the correlation. The relationship obtained was only significant between the rate constant and lipophilic constant.

Article

1999 ◽  
Vol 77 (5-6) ◽  
pp. 1005-1008
Author(s):  
Ayla Khan ◽  
Alexei A Neverov ◽  
Anatoly K Yatsimirsky ◽  
R S Brown
Keyword(s):  
Rate Constant ◽  
Metal Ion ◽  
Order Rate Constant ◽  
Water Proton ◽  
First Order ◽  
Catalytic Rate Constant ◽  
Equilibrium Binding ◽  
Metal Ion Catalysis ◽  
Kinetics Of ◽  
Hydrolysis Of

The kinetics of methanolysis of acetyl imidazole (1) and acetyl pyrazole (2) have been investigated under anhydrous conditions in the presence of Zn(ClO4)2, Co(ClO4)2, and HClO4 at 25°C. In all cases, the plots of the pseudo-first-order rate constant for methanolysis (kobs) vs. [metal ion] or [HClO4] show saturation behavior indicative of equilibrium binding of the M2+ or H+ to the amide. Relative to the spontaneous methanolysis rate constant (ko), the catalytic rate constant obtained at saturation, kcat, is larger for metal-ion catalysis than for H+ catalysis. The (kcatH+/ko) ratio is 10.7 and 1.25 for 1 and 2, respectively, while the (kcatM2+/ko) for these divalent metals varies from 150-fold for 1 to between 700 and 5700-fold for 2. By contrast, in water, proton is far more effective at promoting the hydrolysis of 1 than are metals, the aqueous (kcatH+/ko) ratio being 560, while the (kcatZn2+ /ko) and (kcatNi2+/ko) ratios are 15 and 3.2, respectively.Key words: methanolysis, kinetics, metal-ion catalysis, acetyl imidazole, acetyl pyrazole.

Dissociation kinetics of potassium anion in methylamine

1980 ◽  
Vol 58 (11) ◽  
pp. 1151-1153 ◽  
Author(s):  
Y. Harima ◽  
H. Kurihara ◽  
S. Aoyagui
Keyword(s):  
Rate Constant ◽  
Supporting Electrolyte ◽  
Order Rate Constant ◽  
Dissociation Kinetics ◽  
Potential Sweep ◽  
Solvated Electrons ◽  
Potential Step ◽  
First Order ◽  
Order Rate ◽  
Kinetics Of

The potential-sweep voltammograms of solvated electrons in methylamine containing KI as the supporting electrolyte demonstrate the coexistence of one- and two-electron species in equilibrium. The it1/2 vs. log t curve obtained with potential-step chronoamperometry exhibits a transient part between two plateaux. The analysis of this curve yields the approximate value of 102 s−1 for the first-order rate constant of the dissociation of the two-electron species, K−.

scholarly journals Kinetics of the interaction of chymotrypsin with eglin c

1991 ◽  
Vol 280 (1) ◽  
pp. 27-32 ◽  
Author(s):  
B Faller ◽  
J G Bieth
Keyword(s):  
Rate Constant ◽  
Proteinase Inhibitor ◽  
Enzyme Inhibitor ◽  
Order Rate Constant ◽  
Stopped Flow ◽  
First Order ◽  
Wide Range ◽  
Eglin C ◽  
Pseudo First Order ◽  
Kinetics Of

The kinetics of binding of recombinant eglin c to bovine pancreatic chymotrypsin was studied by conventional and stopped-flow techniques. With nanomolar enzyme and inhibitor concentrations, the inhibition was fast and pseudo-irreversible (k(assoc.) = 4 x 10(6) m-1.s-1 at 7.4 and 25 degrees C). Reaction of the enzyme-inhibitor complex with alpha 1-proteinase inhibitor, an irreversible chymotrypsin ligand, resulted in a slow release of free eglin c, which was monitored by electrophoresis (k(dissoc.) approximately 1.6 x 10(-6) s-1, t1/2 approximately 5 days). The proflavin displacement method and a stopped-flow apparatus were used to monitor the association of chymotrypsin with eglin c under a wide range of inhibitor concentration and under pseudo-first-order conditions. At pH 7.4 and 25 degrees C or 5 degrees C, or at pH 5.0 and 25 degrees C, the pseudo-first-order rate constant of proflavin displacement increased linearly with eglin c up to the highest concentration tested, suggesting a one-step bimolecular association reaction: E + I in equilibrium with EI. However, kassoc. is much lower than the rate constant for a bimolecular reaction and its activation energy (66 kJ.mol-1 at pH 7.4 and 78 kJ.mol-1 at pH 5.0) is far too high for a diffusion-controlled step. The enzyme-inhibitor association may therefore occur via a loose pre-equilibrium complex EI* (Ki* much greater than 5 x 10(-4) M) that rapidly isomerizes (k2 much greater than 2 x 10(3) s-1) into an extremely stable final complex (Ki approximately 4 x 10(-13) M). Unlike other proteinase-inhibitor systems, the chymotrypsin-eglin association is virtually pH-independent.

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