Inhibitors

• An inhibitor is a substance which slows down or stops a reaction by affecting the binding of substrate to the enzymes. Inhibitors can either be reversible and irreversible.
• Examples of irreversible inhibitors include heavy metal ions such as mercury and silver which cause disulphide bonds within the protein structure to break, as a result causing the shape of the active site to change, thus affecting protein activity.
• Another example of an irreversible inhibitor is cyanide that covalently binds to the active site preventing binding of the substrate
• Reversible inhibitors bind to the active site through hydrogen bonds and weak ionic interactions therefore they do not bind permanently. Reversible inhibitors can either be competitive or non-competitive.
• Competitive inhibitors are similar in structure to the substrate molecule therefore they bind to the active site of the enzyme, decreasing its activity as they compete with substrate for the enzyme.
• Competitive inhibitors: . The amount of product formed remains the same, however the rate at which product formation occurs decreases.
• Competitive inhibitors: . The higher the concentration of competitive inhibitor the lower the reaction rate. Increasing the substrate reverses the effect of competitive inhibitors by outcompeting them
• Non-competitive inhibitor does not bind to the active site; it binds at another site on the enzyme known as the allosteric site.
• Binding of the non-competitive inhibitors changes the

  shape of the active site therefore preventing the binding of the substrate. Increasing the concentration of substrate has no effect on non-competitive inhibition.
• Many drugs are inhibitors. Examples include penicillin which is used to fight bacterial infections, it is an inhibitor of enzyme transpeptidase which plays an important role in cell wall formation
• Inhibitor drugs: . Other examples include Ritonavir which is an antiretroviral drug used to treat HIV which inhibits HIV protease which is responsible for assembly of new viral particles and spread of infection.