title: [Certain properties of "biosynthetic" L-threonine dehydratase from subcellular structures of brewers' yeast Saccharomyces carlsbergensis].
abstract: 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.
mesh_terms: D000494:Allosteric Regulation; D006863:Hydrogen-Ion Concentration; D007532:Isoleucine / Q000494:pharmacology; D007700:Kinetics; D008970:Molecular Weight; D012440:Saccharomyces / Q000201:enzymology*; D013347:Subcellular Fractions / Q000201:enzymology; D013913:Threonine Dehydratase / Q000378:metabolism*
chemical_list: D007532:Isoleucine; D013913:Threonine Dehydratase
vernacular_title: Nekotorye svoĭstva "biosinteticheskoĭ" L-treonindegidratazy iz subkletochnykh struktur drozhzheĭ Saccharomyces carlsbergensis.