Negative feedback inhibition is a process where the end product in a biochemical pathway binds with the allosteric site of the first allosteric enzyme in the pathway,the the enzyme then undergoes a conformational change causing it to become inactive (Storey, 2005). This ensures that whilst the end product is available in the surroundings, it is unnecessary for the cell to continue with the process and so it is innactivated until the end product is not available and blocking the allosteric site. This is required to regulate cellular biochemical pathways in order to maintain a healthy cell. Previous studies have explored the importance of understanding the allosteric mechanisms in these biochemical pathways, they have shown that it is of scientific and industrial importance in the development of effective production strains (Lin Chen, 2012). Studies on regulating biosynthesis of isoleucine were one of the first examples of this mechanism. Isoleucine is the end product of a pathway of which threonine is the initiator which is catalysed by threonine dehydratase to form α-Ketobutyrate (I. T. Szamosi, 1994).Threonine dehydratase binds to a seperate site on threonine than isoleucine. TD activity is regulated by negative feedback and is inhibited by the end product isoleucine, (Möckel B, 1994) and activated by the metabolite valine which is from a competing branch . Valine is from a competative pathway where pyruvate reacts with hydroxyethyl-TPP to go through steps and form leucine and valine, valine can also activate threonine dehydratase by binding to its allosteric site (D Travis Gallagher, 1998), this can be shown in experiment by using enzyme mutants.
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