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B6db references: 89076924

type Journal Article
authors Leoncini, R.; Pagani, R.; Marinello, E.; Keleti, T.
title Double inhibition of L-threonine dehydratase by aminothiols
journal Biochim Biophys Acta
ui 89076924
year (1989)
volume 994
number 1
pages 52-8.
keywords Animal
abstract The inhibition of highly purified rat liver L-threonine dehydratase (L- threonine hydro-lyase (deaminating), EC by aminothiols (L- cysteine, D-cysteine, cysteamine) has been studied. Single inhibition experiments evaluated by Lineweaver-Burk and Dixon plots showed, in a given concentration range, partially (parabolic) competitive inhibitions, indicating two binding sites for each inhibitor. Double inhibition experiments revealed that the inhibition was antagonistic, the two inhibitors weakening each other's effect. Formation of EI1 and EI2 binary complexes, and ESI1, ESI2 and EI1I2 ternary complexes was demonstrated, while formation of the quaternary complex ESI1I2 was ruled out. It is assumed that one inhibitor-binding site coincides with the substrate-binding center while the second inhibitor-binding (allosteric, regulatory) site may comprise the pyridoxal-phosphate- binding SH group(s). The comparison between Km and Ki values and the evaluation of intracellular concentrations of L-threonine, L-cysteine and cysteamine suggest a possible physiological role of the inhibition.
last changed 2008/04/01 16:02

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