[Changes in coagulation hemostasis in patients after coronary bypass surgery].

Changes in the coagulation link of hemostasis were studied in 37 patients who had undergone coronary bypass surgery using venous and arterial conduits and in 16 healthy individuals of the same age. The recordings of hemostasiograms were examined before and 14 days after surgery. Prior to coronary bypass surgery, the patients with ischemic heart disease were found to have coagulation hemostatic disorders as moderate hyperfibrinogenemia, fibrinolytic suppression, thrombinemia, and elevated D-dimer concentrations. Postoperatively, hypercoagulation substantially increased with suppressed fibrinolysis and decreased anticoagulants in the protein C system. In this connection, it is necessary to longer use anticoagulants in the postoperative period and to thoroughly monitor hemostasiogram recordings after their discontinuance.

[Kinetic and allosteric properties of highly-purified, biosynthetic L-threonine dehydrogenase from brewer's yeast Saccharomyces carlsbergensis]. / Kineticheskie i allostericheskie svoistva vysokoochishchennoi "biosinteticheskoi" L-treonindegidratazy iz pivnykh drozhzhei Saccharomyces carlsbergensis.

Kinetic and allosteric propeties of highly purified "biosynthetic" L-threonine dehydratase from brewer's yeast S. carlbergensis were studied at three pH values, using L-threonine and L-serine as substrates. It was shown that the plot of the initial reaction rate (v) versus initial substrate concentrations ([S]0 pH 6.5 is hyperbolic (Km=5.0.10-2M), while these at pH 7.8 and 9.5 have a faintly pronounced sigmoidal shape with fast occurring saturation plateaus ([S]0.5= 1.0.10-2 and 0.9.10-2M, respectively). the ratios between L-threonine and L-serine dehydratation rates depend on pH. The kinetic properties and the dependence of substrate specificity on pH suggest that the enzyme molecule undergoes pH-induced (at pH 7.0) conformational changes. The determination of pK values of the enzyme functional groups involved in L-threonine binding demonstrated that these groups have pK is approximately equal to 7.5 and 9.5. The latter group was hypothetically identified as a epsilon-NH2-group of the lysine residue. High concentrations of the allosteric inhibitor (L-isoleucine) decrease the rates of L-threonine and L-serine dehydratation and induce the appearance (at pH 6.5) or increase (at pH 7.9 and 9.5) of homotropic cooperative interactions between the active sites in the course of L-threonine dehydratation. The enzyme inhibition by L-isoleucine increases with a decrease of L-threonine concentrations. Low L-isoleucine concentrations, as well as the enzyme activator (L-valine) stimulate the enzyme at non-saturating substrate concentrations (when L-threonine or L-serine are used as substrates) without normalization of (v) versus [S]0 plots. The maximal activation of the enzyme is observed at pHG 8.5--9.0. It is assumed that the molecule of "biosynthetic" L-threonine dehydratase from brewer's yeast contains two types of sites responsible for the effector binding, i.e., "activatory" and "inhibitory" ones.

[Certain properties of "biosynthetic" L-threonine dehydratase from subcellular structures of brewers' yeast Saccharomyces carlsbergensis]. / Nekotorye svoistva "biosinteticheskoi" L-treonindegidratazy iz subkletochnykh struktur drozhzhei Saccharomyces carlsbergensis.

The paper is concerned with kinetic properties of the "biosynthetic" L-threonine dehydratase (EC 4.2.1.16) solubilized from subcellular structures of brewers' yeast Saccharomyces carlsbergensis in the absence and presence of the allosteric inhibitor, L-isoleucine, at three pH-values (pH 6.5, 7.8 and 9.5). The curve of the initial reaction rate versus initial substrate concentration in the absence of L-isoleucine at pH 6.5 was of hyperbolic character (Km = 5.5.10(-2) M), and at pH 7.8 and 9.5 the kinetic curve had a weakly sigmoidal pattern with a sharp going into the saturation plateaux; the values of [S] 0.5 are 1.10(-2) and 8.7.10(-3) M, respectively. An addition of L-isoleucine to the reaction mixture led to the appearance (at pH 6.5) or to an increase (at pH 7.8 and 9.5) of the sigmoidality of these kinetic curves and to a decrease in values of the maximum reaction rate V. The enzyme sensibility to the inhibitory effect of L-isoleucine decreased with an increase in pH values. Low L-isoleucine concentrations at low substrate concentrations activated the enzyme. The pH optimum for L-threonine dehydratase under study was 9.5-10.0. The enzyme molecular weight is about 300 000.

[Comparative kinetic properties of structure-bound and solubilized L-threonine dehydratase from brewer's yeast]. / Sravnenie kineticheskikh svoistv strukturnosviazannoi i soliubilizirovannoi L-treonindegidratazy iz pivnykh drozhzhei.

It has been shown that L-threonine dehydratase (EC 4.2.1.16) of brewer's yeast Saccharomyces carlsbergensis is localized in the mitochondrial fraction. The enzyme is easily solubilized from the mitochondria by changing the pH and ionic strength of the buffer. Some kinetic properties of structure-bound and solubilized L-threonine dehydratase have been compared at pH 6,5. The kinetic plots of the initial rate of the reaction versus initial substrate concentration for both enzymes have a hyperbolic shape; the affinities of both enzymes for the substrate appear to be similar (Km = 20 mM). Both enzymes are inhibited by L-isoleucine, the shape of the kinetic plots being thereby changed into sigmoidal. Solubilization results in a decrease of the mitochondral enzyme sensitivity to the inhibition by L-isoleucine and in an appearance of cooperative interactions between the allosteric sites.

[Purification, molecular multiplicity and kinetic properties of "biosynthetic" L-threonine dehydratase from E. coli K-12].

"Biosynthetic" L-threonine dehydratase was purified to homogeneous state with yield 29% of total activity from E. coli K-12. The cells were disrupted by means of ultra sound. Nucleic acids and nucleoproteins were precipitated with protamine sulphate, the proteins were fractioned with (NH4)2SO4, by gel filtration through Sephadex G-25 followed by chromatography on DEAE-cellulose using stepways elution by changing the pH-values. The homogenity of the enzyme was shown by polyacrylamide gel disc electrophoresis in the presence of dodecylsulphate. The enzyme consists of equal subunits having a molecular weight about 57000. The polyacrylamide gel disc electrophoresis had shown that the native enzyme consists of a set of oligomeric forms. The multiplisity of molecular organization of the enzyme was relfected in complicated kinetic behavior: at pH greater than 9 on the plots of initial reaction rate (upsilon) versus initial substrate concentration ([S]0) there were four inflexion points (two intermediate plateaux) the position and deepness of which depended on enzyme concentration. Kinetic properties of the highly purified enzyme and the enzyme in crude cell extracts at pH 9.3 and 7.4 were identical. At pH 8,3 on the upsilon versus [S]0 plots appeared two inflexion points (one intermediate plateau), the position of which practically did not depend on enzyme concentration in the reaction mixture but strongly depended on the enzyme concentration in the stock solution. Repeated polyacrylamide gel disc electrophoresis of several oligomeric forms isolated by the first electrophoresis had shown that oligomeric forms underwent a slow polymerization. It is suggested that "biosynthetic" L-threonine dehydratase from E. coli K-12 is a set of multiple oligomeric forms having different kinetic parameters. Probably, each form of the enzyme has a "simple" kinetics characterized by hyperbolic or sigmoidal shape of upsilon versus [S]0 plots. The rate of equilibrium between the oligomeric forms is small in comparison with the enzyme reaction velosity, that lead to the complex kinetic curves appearing as a result of summing up the kinetics inherent to the individual forms.

Studies of homogeneous "biosynthetic" L-threonine dehydratase from Escherichia coli K-12. Some kinetic properties and molecular multiplicity.

"Biosynthetic" L-threonine dehydratase (EC 4.2.1.16) was purified to a homogeneous state with 29% yield of total activity from Escherichia coli K-12. The homogeneity of the enzyme was shown by polyacrylamide gel disc electrophoresis in the presence of dodecyl sulphate. The enzyme consisted of equal subunits having a molecular weight of about 57 000. The polyacrylamide gel disc electrophoresis has shown that the native enzyme consisted of a set of oligomeric forms. The multiplicity of molecular organization of the enzyme was reflected in complicated kinetic behaviour: at pH greater than 9 on the plots of initial reaction rate (v) versus initial substrate concentration ([S]o) there were four inflexion points (two intermediate plateaux), the position and deepness of which depended on enzyme concentration. At pH 8.3 on the v versus [S]o plots appeared two inflexion points (one intermediate plateu), the position of which practically did not depend on enzyme concentration in the reaction mixture, but strongly depended on the enzyme concentration in the stock solution. Repeated polyacrylamide gel disc electrophoresis of several oligomeric forms, isolated by the first electrophoresis, has shown that the oligomeric forms underwent a slow polymerization. It was suggested that "biosynthetic" L-threonine dehydratase from E. coli K-12 is a set of multiple oligomeric forms, having different kinetic parameters. Probably, each form of the enzyme has a "simple" kinetics characterized by hyperbolic or sigmoidal shape of v versus [S]o plots. The rate of equilibrium installation between the oligomeric forms was small in comparison with the enzyme reaction velocity, that lead to the complex kinetic curves, appearing as a result of summing up of the kinetics inherent to theindividual forms.