title: Purification and properties of threonine deaminase from Saccharomyces cerevisiae.
abstract: Threonine deaminase (L-theonine hydro-lyase (deaminating), E.C. 4.2.1.16) has been purified to homogeneity from extracts of Saccharomyces cerevisiae. When purified 1200-fold, the enzyme is homogeneous by the criterion of sodium dodecyl sulfate-polyacrylamide electrophoresis. The reduced and alkylated protein has a molecular weight of approximately 50,000 daltons, one-fourth the value determined previously for the intact enzyme. The purified enzyme exhibits homotropic effects with the substrate; these effects are descresed in the presence of DL-allothreonine, a competitive inhibitor. Half-maximal velocity is achieved at 34 mM L-threonine in the absence of other effectors. L-isoleucine both stimulates at low (0.01-0.05 mM) concentrations and inhibits at high (0.1-1.0 mM) concentrations. Valine activates the enzyme in the absence of isoleucine ; in the presence of isoleucine it reverses inhibition.
mesh_terms: D006836:Hydro-Lyases / Q000302:isolation & purification*; D007532:Isoleucine / Q000494:pharmacology; D007700:Kinetics; D008970:Molecular Weight; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D013237:Stereoisomerism; D013913:Threonine Dehydratase / Q000302:isolation & purification* / Q000378:metabolism; D014633:Valine / Q000494:pharmacology
chemical_list: D007532:Isoleucine; D006836:Hydro-Lyases; D013913:Threonine Dehydratase; D014633:Valine