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K Stocker

Publications and source records attributed to K Stocker.

At least 37 records · Page 2Linked to original sources
PubMed1986

Fast functional protein C assay using Protac, a novel protein C activator.

A simple and rapid clotting method for the quantitative determination of protein C (PC) in plasma consists of the conversion of PC into activated PC (APC) by means of Protac, an activator protein isolated from Agkistrodon contortrix contortrix venom, of the subsequent degradation of factors V and VIII in PC immuno-depleted plasma by the generated APC and of the measurement of the prolongation of the activated partial thromboplastin time (APTT) which is proportional to the amount of PC in the sample. In 33 normal individuals a mean PC level of 97.1% of a normal pooled plasma was found. Comparison with an enzyme-immunoassay for PC in 33 patients with liver disease revealed a good correlation (r = 0.986). Patients under warfarin therapy (n = 34) had a mean PC level of 19.8%; a comparison with the immunological assay (mean value = 55.3%) in the same population suggested that the assay did not co-estimate acarboxy forms of PC. The assay proved to be insensitive to heparin concentration lower than 1 U/ml. Due to its simplicity, it should be suitable for diagnostic routine and monitoring of patients with abnormal PC level, even if under anticoagulation.

Anticoagulants↗
PubMed1986

Determination of factor X activator in the venom of the saw-scaled viper (Echis carinatus).

Factor X activator in Echis carinatus venom was determined by incubating the zymogen 'factor X' with venom, interrupting the activation process by ethylenediaminetetraacetic acid and measuring the generated proteinase 'factor Xa' by means of a synthetic chromogenic substrate. A comparison of factor X- and prothrombin-activating potencies in E. carinatus venoms of five different geographic origins revealed no correlation between these two procoagulant activities.

Factor X↗
PubMed1986

Chromogenic assay for the prothrombin activator ecarin from the venom of the saw-scaled viper (Echis carinatus).

Ecarin, by limited proteolysis and subsequent autocatalytic reactions, causes the conversion of prothrombin into three products with amidolytic activity: meizothrombin, meizothrombin 1 and lpha-thrombin. Ecarin action may be abolished by ethylenediaminetetraacetic acid and the activity of alpha-thrombin can, with a high degree of selectivity, be inhibited by heparin. Thus, ecarin potency may be assayed by measuring the meizothrombin activity generated by ecarin action on human plasma in the presence of heparin. The chromogenic substrate Tosyl-glycyl-L-prolyl-L-arginine-p-nitroanilide (Chromozym TH) is used in this assay.

Animals↗
PubMed1986

Protein C activators in snake venoms.

Venoms of 32 snake species were tested for protein C (PC) activating potency. As measured with the chromogenic PC substrate D-Pro-L-Pro-L-Arg-pNA, eleven venoms were able to generate amidolytic activity from purified bovine PC. In five venom solutions (Bothrops moojeni, B. pradoi, Cerastes cerastes, Vipera lebetina and V. russellii) the PC activating potency was destroyed during 10 min heating at 70 degrees C at pH 3, whereas in six venom solutions (Agkistrodon contortrix contortrix, A. c. mokasen, A. c. pictigaster, Agkistrodon piscivorus, A. p. leucostoma and A. bilineatus) the PC activator was stable under these conditions. PC activator from A. c. contortrix (Protac) was purified to homogeneity and characterized as a single chain polypeptide with a molecular weight of approx. 39-42,000 Dalton. Protac does not exert proteinase activity and is not inhibited by proteinase inhibitors; PC activation with Protac seems to be a stoichiometric reaction. The use of Protac in quantitative PC determination bears significant advantages over the use of thrombin as an activator. In rabbits, i.v. injection of Protac caused a prolonged APTT and did not provoke acute toxic reactions.

Animals↗
PubMed1985

Chromogenic proteinase substrates as possible tools in the characterization of Crotalidae and Viperidae snake venoms.

Proteinase activities have been determined photometrically in 25 different Crotalidae and Viperidae snake venoms by using five different chromogenic proteinase substrates. The activity profiles obtained by listing the identity numbers of substrates hydrolyzed by the venoms in a decreasing potency order remained quite stable within a given snake population. Submission of a venom to various physical and chemical treatments did not alter its activity profile. It is therefore concluded that this simple method of determining proteinase activities could be of help in snake venom characterization, as well as in studying the influence of metallic ions and inhibitors of snake venom proteinases.

Animals↗
PubMed1984

[Modification of the toxicity of Bothrops atrox poison by interventions in the coagulation and kallikrein system of prey].

LD50-determinations with venom mixtures from different age groups of Bothrops atrox were carried out on differently pretreated mice. No differences were seen in the LD50 when comparing untreated mice with mice previously defibrinogenated with batroxobin. Inhibition of the coagulation-, kallikrein-kinin- and fibrinolytic system by pretreatment with batroxobin and aprotinin led to a significantly decreased toxicity of the venom mixtures of all age groups. The age-related difference in toxicity had practically disappeared. Furthermore, the number of mice of the latter group dying within one hour after the venom injection was strongly reduced as compared to untreated and only batroxobin-treated animals. Tests performed on rats showed that the rapidly occurring lethality following the venom injection as a consequence of circulatory disturbances (strong fall of arterial blood pressure, bradycardia, dyspnea), may be prevented almost completely by preincubation of the venom with aprotinin.

Age Factors↗
PubMed1983

Reptilase-test.

Explore the source record for details and available documents.

Batroxobin↗
PubMed1982

Thrombin-like snake venom proteinases.

Proteinases affecting one or several physiological thrombin substrates are current components of Crotalidae and Viperidae venoms. Enzymes causing in vitro coagulation of fibrinogen without affecting other thrombin-susceptible blood constituents as well as enzymes affecting platelets, F. V. VIII and XIII with only minor action on fibrinogen have been isolated. Fibrinogen affecting proteinases may catalyze the release of either fibrinopeptide (Fp) A (e.g. ancrod, batroxobin) or Fp B (Agk, contortrix proteinase) or of both Fp A and B (B. gabonica proteinase). Some of these enzymes are inhibited by AT III-heparin complex (e.g. Agk. contortrix proteinase) some are not inhibited by either AT III-heparin or hirudin (e. g. batroxobin). The application of Fp A releasing venom proteinases into animals causes transformation of fibrinogen into fibrin I monomer which is rapidly degraded by fibrinolysis and thereby leads to a state of afibrinogenaemia. The administered enzyme is gradually bound to serum proteinase-inhibitors and inactivated. A species dependent interaction between venom enzyme, fibrinogen and serum proteinase inhibitors creates specific differences in dose response relationship. Thus, batroxobin isolated from B. moojeni (HOGE) proved to be a superior defibrinogenating agent in man, as compared to the closely related enzyme isolated from B. atrox (L.). LD50 of B. atrox venom in previously batroxobin defibrinogenated mice is not significantly different as compared to normal animals, indicating an only minor role of batroxobin in Bothrops venom poisoning.

Aging↗
PubMed1982

[Simultaneous determination of zymogen activation time and zymogen level using chromogenic substrates in blood coagulation analysis].

The amidolytic activities of plasma generated by means of thromboplastin and Ca++, on the one hand, and by means of partial thromboplastin, a contact activator and Ca++, on the other hand, were determined using synthetic, chromogenic factor Xa substrates with low affinity for thrombin (CH3SO2-D-Leu-Gly-Arg-pNA and CH3SO2-D-Nleu-Gly-Arg-pNA). In this way, the activation process by splitting off the p-nitroaniline was followed. Besides the summary detection of factor Xa was obtained after addition of hirudin. During preincubation with partial thromboplastin and contact acti (Actin) in Ca++-free medium, an amidolytic activity so far unidentified was generated that renders evaluation of the activation process difficult. In the test system with partial thromboplastin, factor Xa could not be determined and the thrombin-like activity that can be inhibited by hirudin did not correspond to the amount of prothrombin present in plasma. In contrast, activation of factor X and prothrombin by thromboplastin and Ca++ could be followed and the content of the two zymogenes could be detected simultaneously. In general, under optimized reaction conditions, automated systems might be developed that would provide additional diagnostic information about determination of clotting time, on the one hand, and about quantitative determination of zymogen, on the other hand.

Calcium↗
PubMed1980

[Sports medical examination of top class chess players (author's transl)].

During an international chess championship tournament in Munich, 14 participants were thoroughly investigated physically in order to find out generally the psychological maximum stress and the autonomic excitability as well as the circulatory conditions during the individual games and to study the metabolic load during the 18 day tournament. Eight of the eleven players who participated in the blood determinations showed at least once during the competition marginal to increased cholesterol levels. In their general physical capacity, their autonomic excitability and their circulatory parameters during the competition the chess players were completely comparable to other sportsmen of the "light athletics" class, so that chess can also rightly be called a class of sport according to these criteria.

Adult↗
PubMed1979

Thrombocytin, a serine protease from Bothrops atrox venom. 1. Purification and characterization of the enzyme.

Thrombocytin, a platelet-activating enzyme from Bothrops atrox venom, has been purified to homogeneity by precipitation with sodium salicylate and chromatography on heparin--agarose. Thrombocytin is a single-chain glycoprotein with a molecular weight of 36 000 which contains 5.6% carbohydrate. It causes platelet aggregation, release of platelet serotonin, and activation of factor XIII. The most sensitive substrate for the amidolytic activity of thrombocytin was Tos-Gly-Pro-Arg-p-nitroanilide hydrochloride. The activity of thrombocytin on this substrate and on platelets was inhibited by diisopropyl fluorophosphate (DFP), soybean trypsin inhibitor, and several arginine chloromethyl ketones. Active site titration with nitrophenyl guanidinobenzoate demonstrated that approximately 86% of the preparation was in the active form. These experiments demonstrate the presence of serine and histidine in the active site of thrombocytin and suggest that thrombocytin is a classical serine protease with a platelet-activating activity similar to thrombin.

Amidohydrolases↗
PubMed1979

Thrombocytin, a serine protease from Bothrops atrox venom. 2. Interaction with platelets and plasma-clotting factors.

Thrombocytin, a serine protease from Bothrops atrox venom, caused platelet aggregation and release of platelet constituents at a concentration of 10(-7) M and clot retraction at a concentration of 2 x 10(-9) M. Thrombocytin was slightly more active when tested on platelets in plasma than on washed platelets suspended in Tyrode--albumin solution. Thrombin was 5 times more active than thrombocytin when tested on platelets in plasma and 50 times more active when tested on washed platelets. The patterns or release induced by thrombocytin and thrombin were similar. Prostaglandin E1 (10(-5) M) produced complete inhibition of platelet release induced by thrombocytin and thrombin. Indomethacin (10(-4) M) was without any effect. Antithrombin III, in the presence of heparin, inhibited the action of thrombocytin on platelets and on a synthetic peptide substrate (Tos-Gly-Pro-Arg-pNA.HCl). formation of an antithrombin III--thrombocytin complex was demonstrated on NaDodSO4--polyacrylamide gel electrophoresis. Hirudin and alpha 1-antitrypsin did not inactivate thrombocytin. Thrombocytin had a low fibrinogen-clotting activity (less than 0.06% that of thrombin). Thrombocytin also caused progressive degradation of the alpha chain of human fibrinogen, and it cleaved prothrombin, releasing products similar to intermediate 1 and fragment 1 produced by thrombin. Thrombocytin activated factor XIII by limited proteolysis and increased the procoagulant activity of factor VIII in a manner analogous to that of thrombin.

Animals↗