scholarly journals A fragment of antithrombin that binds both heparin and thrombin

1986 ◽  
Vol 237 (3) ◽  
pp. 639-646 ◽  
Author(s):  
L Rosenfeld ◽  
I Danishefsky
Keyword(s):  
Rate Constant ◽  
Inhibitory Activity ◽  
Order Rate Constant ◽  
Neutralizing Activity ◽  
Unique Fragment ◽  
High Concentrations ◽  
The One ◽  
A Site ◽  
Polypeptide Chains ◽  
Inhibition Of Thrombin

In order to identify the regions of antithrombin that interact with heparin and thrombin, it was degraded with CNBr and the activities of the isolated products were investigated. These fragments did not exhibit direct thrombin-neutralizing activity; however, one unique fragment was found to bind to heparin-Sepharose and also to interfere with the inhibition of thrombin by intact antithrombin. This fragment was identified as the one consisting of three disulphide-linked polypeptide chains containing residues 1-17, 104-251 and 424-432. At a concentration of 46 nM, this product decreased the heparin-enhanced thrombin-inhibitory activity of antithrombin by half, and completely abolished this inhibition when above 300 nM. In the absence of heparin, the action of antithrombin was not completely nullified by the fragment, even when present at relatively high concentrations. At a given fragment concentration, the extent of inhibition was independent of antithrombin concentration over the range tested. It was found that the fragment decreased the second-order rate constant for the antithrombin-thrombin reaction. Reduction and alkylation of the fragment showed that the above properties reside primarily in the peptide with residues 104-251. It is concluded that this peptide possesses portions of the antithrombin molecule that bind to heparin as well as to a site on thrombin.

Observation of a radical intermediate in the one electron oxidation of 5-methyl-1-thia-5-azacyclooctane by •Br2−

1984 ◽  
Vol 62 (9) ◽  
pp. 1874-1876 ◽  
Author(s):  
Warren Kenneth Musker ◽  
Parminder S. Surdhar ◽  
Rizwan Ahmad ◽  
David A. Armstrong
Keyword(s):  
Aqueous Solution ◽  
Rate Constant ◽  
Half Life ◽  
Cation Radical ◽  
Order Rate Constant ◽  
Type Structure ◽  
Radical Intermediate ◽  
Text Type ◽  
First Order ◽  
The One

The one electron oxidant •Br2− reacts with 5-methyl-1-thia-5-azacyclooctane (4) in aqueous solution at high pH with an overall rate constant of ~2 × 108 M s−1. The radical intermediate produced has a broad maximum at 500 nm with ε = 2400 M−1 cm−1 and at pH 10 decays with a first order rate constant of 2.3 ± 0.3 × 104 s−1, first half-life of 30 ± 5 μs. Its characteristics do not correspond to those of the [Formula: see text] species reported by Asmus and co-workers. The species appears to be the same as the cation radical reported earlier in the one electron oxidation of 4 in acetonitrile. This species is considered to have an [Formula: see text] type structure, which provides transannular stabilization.

scholarly journals STUDIES ON CELL ADHESION

1973 ◽  
Vol 56 (3) ◽  
pp. 659-665 ◽  
Author(s):  
Frederick Grinnell ◽  
Mary Milam ◽  
Paul A. Srere
Keyword(s):  
Cell Adhesion ◽  
Rate Constant ◽  
Adhesive Strength ◽  
Order Rate Constant ◽  
Baby Hamster Kidney ◽  
Bhk Cells ◽  
First Order ◽  
High Concentrations ◽  
Reversible Loss ◽  
Suspended Cells

Normal and transformed baby hamster kidney (BHK) cells attach to Falcon polystyrene with the same first order rate constant. The longer the cells are attached to the bottles, the more difficult they are to remove. Sulfhydryl (—SH) binding reagents inhibit both the attachment of BHK cells and the increase in adhesive strength of attached cells. Attached BHK cells bind fewer molecules of [1-14C]N-ethylamleimide (an —SH binding reagent) than do suspended cells. Incubation of cells with high concentrations of trypsin results in a reversible loss of cell adhesiveness. The recovery of adhesiveness of trypsin-treated cells is inhibited by cycloheximide.

Dissociation kinetics of the solvated electron species in methylamine and methylamine–ammonia mixtures

1982 ◽  
Vol 60 (4) ◽  
pp. 445-455 ◽  
Author(s):  
Y. Harima ◽  
H. Kurihara ◽  
Y. Nishiki ◽  
S. Aoyagui ◽  
K. Tokuda ◽  
...  
Keyword(s):  
Rate Constant ◽  
Ion Pairs ◽  
Order Rate Constant ◽  
Formation Constants ◽  
Dissociation Rate ◽  
Theoretical Treatment ◽  
Solvated Electron ◽  
Dissociation Kinetics ◽  
Potential Sweep ◽  
The One

Potential-sweep voltammetric and potential-step chronoamperometric experiments were made at −50 °C with solvated electrons in methylamine containing LiCl, KI, or CsI. The dissociation rate constants of the ion pairs, (M+•es−), M being alkali metal and es− free solvated electron, were greater than 103 s−1. The pseudo-first-order rate constant of the dissociation of K− into the one-electron species, es− and (K+•es−) in rapid equilibrium, was determined as 40 s−1 by chronoamperometry with 0.5 M KI solutions. The formation constants of K− from the one-electron species determined by chronoamperometry and voltammetry were 4.5 × 104 M−1 and 5.6 × 104 M−1, respectively. An addition of a small amount of ammonia to methylamine caused a decrease in the formation constant of K− and an increase in its dissociation rate constant. The appendix deals with a theoretical treatment of chronoamperograms for an electrode process preceded by the dissociation of a dimer. The boundary value problem was solved by the explicit finite difference method and the analytical method which was based on the concept of reaction layer.

ON THE KINETICS OF THE INHIBITION OF PLASMINOGEN ACTIVATORS BY THE PLASMINOGEN ACTIVATOR INHIBITOR PAI-1

1987 ◽  
Author(s):  
J Chmielewska ◽  
B Wiman
Keyword(s):  
Plasminogen Activator ◽  
Rate Constant ◽  
Rate Constants ◽  
Plasminogen Activator Inhibitor ◽  
Plasminogen Activators ◽  
Order Rate Constant ◽  
Association Reaction ◽  
The One ◽  
Kinetics Of ◽  
Pai 1

The kinetics of the inhibition of the following plasminogen activators: one- and two-chain tissue plasminogen activator (t-PA) and low and high molecular weight urokinase (UK) by PAI-1 was studied. For this purpose direct systems were employed and the reactions were studied in the presence of different concentrations of plasminogen activator chromogenic substrates. The second-order rate constant of the association reaction was estimated from the initial decline in plasminogen activator activity. Determination of the rate constants in the absence of substrates was performed by plotting the rate constants versus the substrate concentrations and extrapolation to zero concentration. The rate constants with all plasminogen activators were very similar and estimated as 2 - 4 x 107 M-1 x s-1. The reactions were also studied in the presence of 6-aminohexanoic acid, lysine, arginine, guanidinium chloride (final concentrations for all substances about 1 mmol/L) and heparin (10 mg/L), without any significant effect on the rate constants. The effect of soluble fibrin (bathroxobin-digested fibrinogen in urea) at 10 - 300 nmol/L was also studied. With one-chain t-PA the rate constant was decreased about 10-fold with the highest fibrin concentration and about 2-fold at 30 nmol/L. In contrast, the reactions with urokinase or two-chain t-PA were not influenced by fibrin at these concentrations. These findings may have a physiological significance: the one-chain t-PA adsorbed to the fibrin surface and actively involved in fibrinolysis would be protected against inactivation by PAI. This phenomenon adds further to the physiological fibrin specificity of one-chain t-PA.

scholarly journals Changes in Thermodynamic Parameters in the Inhibition of Thrombin by Bovine Antithrombin III

1977 ◽  
Author(s):  
Robert H. Yue ◽  
Toby Starr ◽  
Menard M. Gertler
Keyword(s):  
Thermodynamic Parameters ◽  
Rate Constant ◽  
Antithrombin Iii ◽  
Order Rate Constant ◽  
Second Order ◽  
Kcal Mole ◽  
Experimental Conditions ◽  
Reaction Proceeds ◽  
Entropy Of Activation ◽  
Inhibition Of Thrombin

The inhibition of thrombin by isolated bovine antithrombin III (1, 200 units/mg of protein) was studied under a variety of experimental conditions. This inactivation reaction follows a second-order reaction and the rate constant depends on a number of parameters. The second-order rate constant decreases with an increase of thrombin concentration. However, at a constant initial concentration of thrombin, the measured amount of antithrombin III present in a sample is directly proportional to the aliquot of the sample. The rate of inactivation was investigated with changes of temperature. For example, at an initial thrombin concentration of 6. 8 units/ml and antithrombin III concentration of 4. 2 units/ml, the reaction proceeds with Ea of 25 Kcal/mole and Δ S‡ of 42 e. u. /mole. In the presence of 0. 0015 unit of heparin/ml and with similar concentrations of thrombin and antithrombin III, the reaction proceeds with Ea of 16 Kcal/mole and Δ S‡ of 14 e.u. /mole. Therefore, the presence of heparin causes a lowering of the activation energy and a concomitant decrease in the entropy of activation. This change in the thermodynamic parameters allows the inactivation reaction to proceed much faster in the presence of heparin. The effect of heparin may be the result of solvent macromolecular interaction in this inhibition reaction.

Development of Sustained Release Multi-Component Microparticulate System of Diclofenac Sodium and Tizanidine Hydrochloride

1970 ◽  
Vol 1 (1) ◽  
pp. 97-105
Author(s):  
Kamlesh Dashora ◽  
Shailendra Saraf ◽  
Swarnalata Saraf
Keyword(s):  
Particle Size ◽  
Sustained Release ◽  
Cellulose Acetate ◽  
Rate Constant ◽  
Diclofenac Sodium ◽  
Order Rate Constant ◽  
Anomalous Transport ◽  
First Order ◽  
Sem Study ◽  
Transport Type

Sustained released tablets of diclofenac sodium (DIC) and tizanidine hydrochloride (TIZ) were prepared by using different proportions of cellulose acetate (CA) as the retardant material. Nine formulations of tablets having different proportion of microparticles developed by varied proportions of polymer: drug ratio ‘’i.e.’’; 1:9 -1:3 for DIC and 1:1 – 3:1 for TIZ. Each tablet contained equivalent to 100 mg of DIC and 6mg of TIZ. The prepared microparticles were white, free flowing and spherical in shape (SEM study), with  the particle size varying from 78.8±1.94 to 103.33±1.28 µm and 175.92± 9.82 to 194.94±14.28µm for DIC  and TIZ, respectively.  The first order rate constant K1 of formulations were found to be in the range of  K1 = 0.117-0.272 and 0.083- 0.189 %hr-1for DIC and TIZ, respectively. The value of exponent coefficient (n) was found to be in the range of 0.6328-0.9412  and 0.8589-1.1954 for DIC and TIZ respectively indicates anomalous  to  non anomalous transport type of diffusions among different formulations

scholarly journals Alkylation of glyceraldehyde-3-phosphate dehydrogenase with haloacetylphosphonates. An unusual pH-dependence

1991 ◽  
Vol 275 (3) ◽  
pp. 767-773 ◽  
Author(s):  
Y K Li ◽  
J Boggaram ◽  
L D Byers
Keyword(s):  
Isotope Effect ◽  
Rate Constant ◽  
Ph Dependence ◽  
Thiol Group ◽  
Order Rate Constant ◽  
Acidic Group ◽  
Irreversible Inhibitors ◽  
Effects Of Ph ◽  
Solvent Isotope ◽  
Bell Shaped Curve

Two new alkylating reagents, chloro- and bromo-acetylphosphonate, were found to be very effective thiol-blocking reagents. The pH-dependence of the reaction of BAP with 2,4-dinitrothiophenol (25 degrees C, I 0.5) shows a tailing bell-shaped curve (with a plateau at high pH) characteristic of two ionizing groups: the thiol group (pKa 3.2) and the phosphonate group (pKa2 4.6). The rate constant for the reaction of the monoanionic inhibitor with dinitrothiophenolate (k2 = 7 M-1.s-1) is 120 times larger than that of the dianionic species. The haloacetylphosphonates were found to be irreversible inhibitors of glyceraldehyde-3-phosphate dehydrogenase from a variety of sources. They react with the active-site thiol group (Cys-149) and are half-site reagents with yeast glyceraldehyde-3-phosphate dehydrogenase. Thus, when two of the identical four subunits are modified the enzyme is catalytically inactive. The effects of pH (7-10), 2H2O and NAD+ on the reaction with the yeast enzyme were examined in detail. NAD+ enhances the alkylation rates. The second-order rate constant does not show a simple sigmoidal dependence on pH but rather a tailing bell-shaped curve (pKa 7.0 and 8.4) qualitatively similar to that obtained with dinitrothiophenol. There is no significant solvent isotope effect on the limiting rate constants and a normal isotope effect on the two pKa values. The results are consistent with the more reactive enzyme species containing a thiolate and an acidic group that may either donate a proton to the dianionic haloacetylphosphonate or orient the inhibitor.

scholarly journals Specificity of activated human protein C

1985 ◽  
Vol 230 (2) ◽  
pp. 497-502 ◽  
Author(s):  
S R Stone ◽  
J Hofsteenge
Keyword(s):  
Amino Acid ◽  
Rate Constant ◽  
Amino Acid Residue ◽  
Protein C ◽  
Activated Protein C ◽  
Order Rate Constant ◽  
Human Protein ◽  
Functional Protein ◽  
Hydrophobic Residues ◽  
Apolar Residue

Peptide p-nitroanilide substrates and peptidylchloromethane inhibitors were used to examine the specificity of activated human Protein C. Substrates with arginine in the P1 position had the highest activity. The best substrates and inhibitors, as judged by the second-order rate constant for their interaction with the enzyme, had an apolar residue in the P2 position. In contrast with thrombin [Kettner & Shaw (1981) Methods Enzymol. 80, 826-842], activated Protein C was able to accommodate large hydrophobic residues such as phenylalanine and leucine in the P2 position. In the P3 position, the enzyme preferred an apolar D-amino acid residue. The results of the present study have also indicated a suitable substrate and inhibitor to be used in the assay of functional protein C and of thrombomodulin.

scholarly journals The T788G Mutation in thecyp51CGene Confers Voriconazole Resistance in Aspergillus flavus Causing Aspergillosis

2012 ◽  
Vol 56 (5) ◽  
pp. 2598-2603 ◽  
Author(s):  
Wei Liu ◽  
Yi Sun ◽  
Wei Chen ◽  
Weixia Liu ◽  
Zhe Wan ◽  
...  
Keyword(s):  
Aspergillus Flavus ◽  
Resistant Strain ◽  
Antifungal Susceptibility ◽  
Gene Replacement ◽  
Content Type ◽  
Replacement Method ◽  
First Choice ◽  
The One ◽  
A Site ◽  
First Time

ABSTRACTWith voriconazole (VRC) being approved as the first choice in treating invasive aspergillosis (IA) and its increasing use in treatment, a VRC-resistant strain ofAspergillus flavus, the second leading cause of IA afterAspergillus fumigatus, has emerged. The VRC-resistant strain ofA. flavuswas isolated for the first time from the surgical lung specimen of an IA patient with no response to VRC therapy. In order to ascertain the mechanism of VRC resistance, the azole target enzyme genes in this strain ofA. flavuswere cloned and sequenced, and 4 mutations generating amino acid residue substitutions were found in thecyp51Cgene. To further determine the role of this mutated gene for VRC resistance inA. flavus, anAgrobacterium tumefaciens-mediated gene replacement approach was applied. Consequently, the mutatedcyp51Cgene from thisA. flavusstrain was proven to confer the VRC resistance. Finally, to discern the one out of the four mutations in thecyp51Cgene that is responsible for contributing to VRC resistance, a site-directed gene mutagenesis procedure combined with a gene replacement method was performed. As a result, the T788G missense mutation in thecyp51Cgene was identified as responsible for VRC resistance inA. flavus. These findings indicated that the detection of this mutation inA. flavuscould serve as an indicator for physicians to avoid the use of VRC during IA treatment. Further comprehensive surveillance for antifungal susceptibility, as well as intensive study on the mechanism of azole resistance inA. flavuscausing IA, would be required to fully understand this mechanism.

scholarly journals The reactivities and ionization properties of the active-site dithiol groups of mammalian protein disulphide-isomerase

1991 ◽  
Vol 275 (2) ◽  
pp. 335-339 ◽  
Author(s):  
H C Hawkins ◽  
R B Freedman
Keyword(s):  
Rate Constant ◽  
Ph Dependence ◽  
Order Rate Constant ◽  
Second Order ◽  
Native Enzyme ◽  
Liver Protein ◽  
Thiol Groups ◽  
Protein Disulphide Isomerase ◽  
Order Rate ◽  
Reactive Groups

1. The number of reactive thiol groups in mammalian liver protein disulphide-isomerase (PDI) in various conditions was investigated by alkylation with iodo[14C]acetate. 2. Both the native enzyme, as isolated, and the urea-denatured enzyme contained negligible reactive thiol groups; the enzyme reduced with dithiothreitol contained two groups reactive towards iodoacetic acid at pH 7.5, and up to five reactive groups were detectable in the reduced denatured enzyme. 3. Modification of the two reactive groups in the reduced native enzyme led to complete inactivation, and the relationship between the loss of activity and the extent of modification was approximately linear. 4. Inactivation of PDI by alkylation of the reduced enzyme followed pseudo-first-order kinetics; a plot of the pH-dependence of the second-order rate constant for inactivation indicated that the essential reactive groups had a pK of 6.7 and a limiting second-order rate constant at high pH of 11 M-1.s-1. 5. Since sequence data on PDI show the presence within the polypeptide of two regions closely similar to thioredoxin, the data strongly indicate that these regions are chemically and functionally equivalent to thioredoxin. 6. The activity of PDI in thiol/disulphide interchange derives from the presence of vicinal dithiol groups in which one thiol group of each pair has an unusually low pK and high nucleophilic reactivity at physiological pH.

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