The Reactivity of One Essential Cysteine as a Conformational Probe in Escherichia coli Tryptophanase

摘要: It is first shown that the inactivation of Escherichia coli apotryptophanase by N-ethylmaleimide results from labeling a single particularly reactive cysteine per protomer. The reactivity this under various conditions investigated and indicate protein can exist two classes conformation: one, corresponding to inactive protein, in which reactive, second, active enzyme, where masked. The rate isomerization step involved change conformation measured stopped-flow technique (τ= 0.4 s). Finally, used characterize dimeric holotryptophanase (i.e. dissociated form enzyme obtained as transient species between apoenzyme natural tetrameric holoenzyme). By criterion, it falls class ‘inactive’ conformations. These are discuss influence quaternary structure on functional conformational properties tryptophanase nature activation its cofactor specific cations.