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 BIOCHEMISTRY
 
FACTORS THAT AFFECT ENZYME ACTIVITY

The effect of enzyme inhibition

Irreversible inhibitors: These combine with the functional groups of the amino acids in the active site, irreversibly.

 Examples: nerve gases and pesticides, containing organophosphorus, combine with serine residues in the enzyme acetylcholine esterase.

Reversible inhibitors: These can be washed out of the solution of enzyme by dialysis. There are two categories.

Competitive: These compete with the substrate molecules for the active site.

The inhibitors action is proportional to its concentration.

Usually this type of inhibitor resembles the substrate’s structure closely

If more substrate is added, the effect of the inhibitor is reduced.

Non-competitive: These are not influenced by the concentration of the substrate. It inhibits by binding irreversibly to the enzyme but not at the active site

Examples
Cyanide combines with the Iron in the enzymes cytochrome oxidase.
Heavy metals, Ag or Hg, combine with –SH groups.
These can be removed by using a chelating agent such as EDTA.

Applications of inhibitors
 Negative feedback See end point or end product inhibition
Poisons snake bite, plant alkaloids and nerve gases.
Medicine antibiotics, sulphonamides, sedatives and stimulants

© Paul Billiet 2008