Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.5 (thrombin)
 33,306 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

By devising and applying quantitative methods for the assay of thrombin and autoprothrombin C and by developing techniques for their purification, it was possible to obtain information about the function and properties of antithrombin. The inhibitor is a protein for which the initial purification steps consist of removing fibrinogen from plasma by heating to 56 degrees for 3 min, removing prothrombin complex by absorption on barium carbonate, absorbing the antithrombin on aluminum hydroxide, and eluting with phosphate buffer. Antithrombin is limited in its capacity to neutralize thrombin activity, and, under some conditions, the rate of inhibition was accelerated, but equivocal results were involved. Heparin cofactor was found to be essential for retarding the formation of thrombin, and, by inference, it is essential for retarding the formation of autoprothrombin C. Heparin cofactor and antithrombin III are the same. Thrombin absorbs on fibrin, and this has been referred to as the "antithrombin I effect." Interference with the thrombin-fibrinogen reaction by mixtures of antithrombin III and heparin is called the "antithrombin II henomenon." The acceleration of thrombin inactivation at the time thrombin forms is called the "antithrombin IV effect." It was discovered that antithrombin III neutralizes thrombin, as well as autoprothrombin C. The inhibitor and the enzyme form a mutual depletion system. To assay for antithrombin III, a standard quantity of thrombin (about 1,100U/ml) was reacted with antithrombin III for 2 hr. The percent thrombin inactivated was then measured. In random samples of human blood, a wide range of antithrombin III concentration was found. The inhibitor is relatively stable in plasma and serum. It is not changed in concentration when Dicumarol therapy is instituted. Ether extraction of plasma reduces antithrombin III activity. Seitz filtration of plasma did not remove activity. Under special conditions, antithrombin III enhances esterase activity of thrombin. Under special conditions, thrombin regenerates from the thrombin-antithrombin III complex. Antithrombin III neutralizes the activity of prethrombin-E and thrombin-E; consequently, an active histidine center found in the B1 chain of thrombin is not essential for the binding of antithrombin. Autoprothrombin II-A activity was neutralized by antithrombin III. Autoprothrombin C was found to be neutralized by antithrombin III; the amounts required varied with the molecular forms of autoprothrombin C. Thrombin and autoprothrombin C apparently occupy the same binding sites on antithrombin III. An equation was developed to account for all the known characteristics of antithrombin III functions. The kinetic aspects of thrombin neutralization were found to correspond exactly with those of autoprothrombin C. Antithrombin III is a high-capacity inhibitor of the two most powerful enzymes in blood coagulation.
 ...
PMID:Antithrombin III: a backward glance o'er travel'd roads. 4 4

Antithrombin activity has been identified in intact washed human platelets. An apparent activity was demonstrated at platelet concentrations above 0.31 X 10(9)/ml, when platelet suspensions were incubated with 2.0 NIH units/ml of thrombin. Neither red cells nor white cells revealed antithrombin activity. No significant loss of the platelet antithrombin activity was observed after ten successive washings or after treatment of platelets with antibodies to antithrombin III or alpha2-macroglobulin. Almost the same amount of antithrombin activity as normal platelets was demonstrated in the platelets from an afibrinogenemic patient. Pre-treatment of platelets with trypsin, papain, and neuroaminidase reduced the activity significantly, whereas lipase was without effect. The platelet antithrombin reacted with thrombin in less than 3 seconds, and this rapid reaction of platelet antithrombin was different from that of plasma antithrombin III or fibrinogen. The thrombin-like clotting activity of ancrod was inhibited by fibrinogen but not platelets. Also, unlike plasma antithrombin III or fibrinogen, brief exposure to heat (56 degrees C or 60 degrees C) reduced considerable amounts of platelet antithrombin activity. These results suggest that platelets possess a specific antithrombin with different characteristics from other known antithrombins.
 ...
PMID:Antithrombin activity of intact human platelets. 5 97

A new rapid method for assaying total antithrombin activity has been developed based on the inactivation of thrombin incorporated into an agarose gel, during the radial diffusion of plasma in the gel. The area of thrombin inactivation is subsequently observed by the coagulation of fibrinogen in a separate agarose gel layer poured over the thrombin gel. The method is described in detail and its accuracy assessed with respect to other antithrombin assays. Using specific antisera to alpha2-globulin (antithrombin III), alpha2-macroglobin and alpha1-antitrypsin, total antithrombin activity measured by this assay consisted of 47% alpha2-globulin, 29% alpha2-macroglobulin and 26% alpha1-antitrypsin.
 ...
PMID:A new assay for the measurement of total progressive antithrombin. 5 64

A method for the differential determination of plasma antithrombins, antithrombin III and alpha2 macroglobulin, is described. The method is based on the selective inactivation of plasma alpha2 macroglobulin by treatment with 0-1 M methylamine for 10 minutes at 37 degrees C and on the observation that antithrombin III and alpha2 macroglobulin inhibited in defibrinated plasma low concentrations of thrombin without mutual interference and according to pseudo-first order reaction. In healthy subjects antithrombin III was shown to account for about 70% of the total antithrombin activity. But in patients with liver cirrhosis, where low levels of total antithrombin activity were observed, the relative contribution of antithrombin III was found to be noticeably lower.
 ...
PMID:A method for the differential determination of plasma antithrombins. 5 20

Large amounts of saturated fats (S.F.) or unsaturated fats (U.S.F.) were given to healthy volunteers at a single meal. The heparin thrombin clotting-time, which may measure platelet factor 4 released from platelets into the plasma, was shortened after S.F. and prolonged after U.S.F. The antithrombin clotting activity decreased after S.F. and increased after U.S.F. The platelet-count decreased and the platelet volume increased after both S.F. and U.S.F.
 ...
PMID:Acute platelet changes after large meals of saturated and unsaturated fats. 5 45

An assay technic for measuring heparin cofactor activity in which antithrombin activity can be assessed without plasma attenuation even in the presence of therapeutic levels of heparin is presented. Heparin-activated anti-thrombin activity was markedly depressed in plasmas of four patients with disseminated intravascular coagulation and in ten patients with cirrhosis. Residual activity in those plasmas appeared qualitatively normal, and no inhibitor (platelet factor IV activity) was observed. Plasmas from patients with disseminated intravascular coagulation and cirrhosis required more heparin to obtain in vitro clotting time prolongation equivalent to normal.
 ...
PMID:Minimal heparin cofactor activity in disseminated intravascular coagulation and cirrhosis. 6 Aug 79

Inactivation of alpha- and beta-thrombin by antithrombin-III and heparin was studied, since it had been suggested that two forms of thrombin exist with respect to heparin sensitivity (Machovich 1975b). It was found that the inactivation rates of alpha- and beta-thrombin by antithrombin were different, namely alpha-thrombin was more sensitive to antithrombin than beta-thrombin. Heparin facilitated the complex formation between alpha-thrombin and antithrombin-III, whereas beta-thrombin inactivation was only slightly affected. Furthermore, heparin protected alpha-thrombin against the inactivating effect of heat, while beta-thrombin lost its activity during the heat treatment. These findings suggest that the formation of beta-thrombin in blood circulation may have an important role in thrombosis predisposition.
 ...
PMID:Inactivation of alpha- and beta- thrombin by antithrombin-III and heparin. 6 98

The thrombin time of normal citrated plasma is progressively prolonged on incubation in open glass tubes at 37 degrees C. The phenomenon is dependent on the temperature and duration of incubation, on the pH, and on the concentration of calcium ions present. Platelet-rich citrated plasma fails to exhibit augmented antithrombin activity when similarly incubated, and the addition of washed platelets to platelet-poor plasma inhibits this activity. The clot retarding action of incubated plasma against thrombin is also manifested against Arvin (Ancrod), but not against Reptilase-R. This thrombin time lengthening may be inhibited by incubation with anti-antithrombin III antiserum thus indicating that the phenomenon of thrombin time lengthening is consistent with enhanced activity of antithrombin III. It is unlikely that alterations in the activity of alpha2-macroglobulin, is important in the reduced thrombin-coagulability of incubated plasma. Interference with the polymerisation of fibrin monomers by the physico-chemical changes may contribute to the observed phenomenon.
 ...
PMID:The reversible antithrombin activity of incubated plasma. 6

Methods for the measurement of thrombin and plasma antithrombin, by end point determination at a semi micro level and also by rate assay measurement in a fully automated system have been devised using the thrombin specific chromogenic substrate, H-D-Phe-Pip-Arg-p-nitroanilide. Preliminary defibrination of plasma is avoided in both methods. The semi micro method has been correlated with antitrhombin measured in plasma of postoperative patients by established clotting and immunological assays. The automated method has been found to be highly reproducible and to have less scatter than the other procedures.
 ...
PMID:Methods for semi micro or automated determination of thrombin, antithrombin, and heparin cofactor using he substrate, H-D-Phe-Pip-Arg-p-nitroanilide-2HCl. 7 Feb 86

Inactivation of alpha- and beta-thrombin by alpha 2-macroglobulin, by alpha 1-proteinase inhibitor and by antithrombin-III and heparin was studied. The amount of alpha- and beta-thrombin inactivated by antithrombin-III was proportional to the concentration of the inhibitor, but the inactivation rates of the two forms of thrombin were different. Heparin facilitated complex-formation between alpha-thrombin and antithrombin-III, whereas inactivation of beta-thrombin by antithrombin was only slightly influenced, even at a heparin concentration two orders of magnitude higher. alpha 2-Macroglobulin inhibited both alpha- and beta-thrombin activity similarly, i.e. the amount of alpha- and beta-thrombin inactivated as well as the rates of their inhibition were the same. alpha 1-Proteinase inhibitor also formed a complex with alpha- and beta-thrombin, similarly to antithrombin-III, although the inactivation of the enzyme needed high inhibitor concentration and long incubation time. These results suggest that the inactivation of beta-thrombin, if it occurs in the plasma, is also controlled by plasma inhibitors.
 ...
PMID:Inactivation of alpha- and beta-thrombin by antithrombin-III, alpha 2-macroglobulin and alpha 1-proteinase inhibitor. 7 48


1 2 3 4 5 6 7 8 9 10 Next >>