L4 - enzyme inhibitors

• Reversible inhibitors:

  -an enzymes activity can be reduced or stopped, temporarily, by a reversible inhibitor

  -there are two types of reversible inhibitors; competitive and non competitive
• Enzyme inhibitors reduce the rate of enzyme controlled reactions by preventing the formation of enzyme-substrate complexes
• Competitive inhibitors: able to prevent the formation of an enzyme-substrate complex by fitting into the enzyme's active site to form an enzyme-inhibitor complex
• Competitive inhibitors have a similar shape to that of the substrate molecules and therefore compete with the substrate for the active site
• An increase in the relative concentration of competitive inhibitor molecules will mean that more inhibitors collide with active sites and the effect of inhibition will be greater
• Increasing the concentration of an inhibitor reduces the rate of reaction and eventually, if inhibitor concentration continues to be increased, the reaction will stop completely
• Most of the enzyme inhibition by competitive inhibitors is reversible, meaning that the competitive inhibitor detaches and leaves the active site once the formation of the ESC has been inhibited
• For competitive inhibitors, countering the increase in inhibitor concentration by increasing the substrate concentration can increase the rate of reaction once more (more substrate molecules man they are more likely to collide with enzymes and form enzyme-substrate complexes)
• Non-competitive inhibitors bind to the enzyme at an alternative site, which alters the shape of the active site and therefore prevent the substrate from binding to it
• Non-competitive inhibitors bind to the enzyme in a region away from the active site, which is known as the allosteric site
• The binding of a non-competitive inhibitor to the enzyme at the allosteric site changes the shape of the active site, meaning that it is no longer complementary to the substrate molecule and this prevents enzyme-substrate complexes from forming
• A non-competitive inhibitor binds to an enzyme at the allosteric site and disrupts the tertiary structure. This changes the shape of the active site so that it is no longer complementary to the substrate and prevents the formation of an ESC
• As non-competitive inhibitors change the shape of the active site, increasing the substrate concentration will not allow the uninhibited maximum rate of reaction to be attained like it did with competitive inhibitors
• The action of some inhibitors is describes as irreversible as it doesn’t dissociate from the enzyme following inhibition of the formation of the ESC
• Non reversible inhibitors:

  -some inhibitors can form covalent bonds with enzymes, inhibiting them permanently

  -these are known as non reversible or irreversible inhibitors

  -if this type of inhibition occurs in a living cell or organism it will result in the complete inactivation of the enzyme
• Complete inactiva Tati on of an enzyme can be dangerous as it can cause the biological reaction the enzymes is catalysing to be completely stopped. The only way to avoid this is for the cell or organism to produce more of the enzyme being inhibited, which can only be achieved by transcribing and translating the gene(s) for that enzyme, which is a relatively slow process
• End product inhibition is a form of negative feedback by which metabolic pathways can be controlled
• End product inhibition and the control of metabolic pathways:

  -reversible inhibitors can act as regulators in metabolic pathways

  -metabolic reactions must be very tightly controlled and balanced

  -metabolic reactions can be controlled by using the end product of a particular sequence of metabolic reactions as a non competitive, reversible inhibitor
• Metabolic reactions must be very tightly controlled and balanced so that no single enzyme can ‘run wild’ and continuously generate more and more of a particular product
• End product inhibition and the control of metabolic pathways:

  -the final product in a series of reactions inhibits an enzyme from an earlier step in the sequence

  -the product binds to an allosteric site and temporarily inactivates the enzyme

  -as the enzyme can no longer function, the reaction sequence is halted and the rate of product formation is decreased