End-Product Inhibition

End-product inhibition is a way that a cell controls a metabolic pathway: the final product of the pathway inhibits an enzyme that acts near the start of it. It is an example of negative feedback.Most metabolic pathways are a chain of reactions, each catalysed by its own enzyme:A → B → C → D (end product)If the end product D builds up, it binds to the first enzyme (enzyme 1, which converts A to B). This slows or stops the whole pathway, so less D is made. When D is used up, fewer enzyme 1 molecules have D bound, enzyme 1 becomes active again and production restarts. The amount of end product is therefore kept roughly constant and matched to the cell's needs.The end product usually binds to an allosteric site on the first enzyme, not to the active site. This changes the shape of the active site so the substrate fits less well, so it works like non-competitive inhibition. The binding is weak and reversible, which is essential: the pathway must be able to switch back on.Inhibiting the first enzyme rather than a later one means the cell does not waste substrate and energy making intermediates (B and C) that it does not need.A well-known example is the production of ATP in respiration. ATP inhibits phosphofructokinase, an enzyme early in glycolysis, so when a cell has plenty of ATP, glucose is broken down more slowly.