[Intermediate plateaux in kinetics of the reaction catalyzed by biodegradative L-threonine dehydratase from Escherichia coli].

Title[Intermediate plateaux in kinetics of the reaction catalyzed by biodegradative L-threonine dehydratase from Escherichia coli].
Publication TypeJournal Article
Year of Publication1975
AuthorsSinelnikova EM, Dvoretskova TV, Kagan ZS
JournalBiokhimiia
Volume40
Issue3
Pagination645-51
Date Published1975 May-Jun
ISSN0320-9725
KeywordsAdenosine Monophosphate, Allosteric Regulation, Allosteric Site, Binding Sites, Escherichia coli, Hydro-Lyases, Hydrogen-Ion Concentration, Kinetics, Protein Binding, Threonine Dehydratase
Abstract

It has been shown that for the reaction catalyzed by "biodegradative" L-threonine dehydratase from E. coli strains K-12 and 980 in 0.5 M phosphate-carbonate buffer, pH 8.4 and pH 9.5, the plots of initial reaction rate (v) versus the initial substrate concentration ([S]0 are characterized by several inflection points, i. e. an intermediate plateau. The plot of v versus the allosteric activator (AMP) concentration have very complicated shapes: there are several inflection points, and also the maximum at L-threonine concentration equal to 3-10(2) and 5-10(-2) M. High AMP concentrations inhibit the enzyme at high substrate concentrations. The reduced glutathion dose not influence the enzyme and does not alter the activating effect of AMP. On the basis of the data obtained it is proposed that the substrate and AMP shift the equilibrium between multiple oligomeric enzyme forms differing in catalytic activity and kinetic manifestations of allosteric interactions between the active and allosteric AMP-binding sites towards polymerization. Thus, the functioning the enzyme under study is discussed in the frames of the model of dissociating regulatory enzymes with multiple intermediate oligomeric forms.

Alternate JournalBiokhimiia
PubMed ID1111