19-10-2012, 03:15 PM
ENZYME INHIBITION
ENZYME INHIBITION.ppt (Size: 374 KB / Downloads: 38)
Inhibitors
Inhibitors are chemicals that reduce the rate of enzymic reactions
The are usually specific and they work at low concentrations
They block the enzyme but they do not usually destroy it
Many drugs and poisons are inhibitors of enzymes in the nervous system
The effect of enzyme inhibition
Irreversible inhibitors: 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
Applications of inhibitors
Negative feedback: end point or end product inhibition
Poisons snake bite, plant alkaloids and nerve gases
Medicine antibiotics, sulphonamides, sedatives and stimulants
ATP is the end point
This reaction lies near the beginning of the respiration pathway in cells
The end product of respiration is ATP
If there is a lot of ATP in the cell this enzyme is inhibited
Respiration slows down and less ATP is produced
As ATP is used up the inhibition stops and the reaction speeds up again
A change in shape
When the inhibitor is present it fits into its site and there is a conformational change in the enzyme molecule
The enzyme’s molecular shape changes
The active site of the substrate changes
The substrate cannot bind with the substrate
Negative feedback is achieved
The reaction slows down
This is not competitive inhibition but it is reversible
When the inhibitor concentration diminishes the enzyme’s conformation changes back to its active form
Phosphofructokinase
This enzyme an active site for fructose-6-phosphate molecules to bind with another phosphate group
It has an allosteric site for ATP molecules, the inhibitor
When the cell consumes a lot of ATP the level of ATP in the cell falls
No ATP binds to the allosteric site of phosphofructokinase
The enzyme’s conformation (shape) changes and the active site accepts substrate molecules
The respiration pathway accelerates and ATP (the final product) builds up in the cell
As the ATP increases, more and more ATP fits into the allosteric site of the phosphofructokinase molecules
The enzyme’s conformation changes again and stops accepting substrate molecules in the active site
Respiration slows down