Question

How does the end product of a metabolic pathway prevent the functioning of an enzyme earlier in the pathway? What type of inhibition would this process be?

Answer 1

• End products of metabolic pathways acts as allosteric inhibitors of the enzymes which are required for their own synthesis i.e. for formation of intermediates which are required for production of end product.
• End product inhibits it's own synthesis by the changing the confirmation (3D structure ) of substrate binding site and decreases affinity of enzyme binding site to substrate which inhibits binding of substrate to enzyme therefore inhibiting metabolic pathway.
• For eg. In amino acid synthesis pathway, in which isoleucine is formed from threonine, isoleucine (end product) inhibits the enzyme threonine deaminase which is required for synthesis of isoleucine from threonine.
• This mechanistic loop of inhibition, in which a molecule inhibits its own synthesis is known as feedback inhibition or end product inhibition.
• Inhibition by the end product is non competitive i.e. the end product binds to a site on enzyme different from substrate binding site and neither competes to the substrate binding site on enzyme(competitive inhibition) nor binds to the enzyme substrate complex (uncompetitive inhibition).