<P> Non-competitive inhibition models a system where the inhibitor and the substrate may both be bound to the enzyme at any given time . When both the substrate and the inhibitor are bound, the enzyme - substrate - inhibitor complex cannot form product and can only be converted back to the enzyme - substrate complex or the enzyme - inhibitor complex . Non-competitive inhibition is distinguished from general mixed inhibition in that the inhibitor has an equal affinity for the enzyme and the enzyme - substrate complex . For example in the enzyme - catalyzed reactions, phosphoenol is catalyzed by pyruvate kinase into pyruvate . Alanine is an amino acid that inhibits the enzyme pyruvate kinase during glycolysis . In glycolysis, the end product is pyruvate . However alanine is a non-competitive inhibitor, therefore it doesn't need an active site to bind to the substrate to still become the final product . </P> <P> PhophoenolPyruvate → k i n a s e P y r u v a t e Pyruvate → i n h i b i t o r n o n c o m p e t i t i v e Alanine (\ displaystyle (\ ce (PhophoenolPyruvate -> (Pyruvate) (kinase) Pyruvate -> (noncompetitive) (inhibitor) Alanine))) </P> <P> The most common mechanism of non-competitive inhibition involves reversible binding of the inhibitor to an allosteric site, but it is possible for the inhibitor to operate via other means including direct binding to the active site . It differs from competitive inhibition in that the binding of the inhibitor does not prevent binding of substrate, and vice versa, it simply prevents product formation for a limited time . </P> <P> This type of inhibition reduces the maximum rate of a chemical reaction without changing the apparent binding affinity of the catalyst for the substrate (K--see Michaelis - Menten kinetics). </P>

Where do noncompetitive inhibitors bind on an enzyme
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