Enzyme Inhibition (Quiz 1) Flashcards
____________ are chemicals that reduce the rate of enzymic reactions.
- are usually specific and they work at low concentrations.
- block the enzyme, but they do not usually destroy it.
- Many drugs and poisons are ______ of enzymes in the nervous system.
Note: Same Answer
Inhibitors
Type of Enzyme Inhibitors (2)
- Nonspecific
- Specific
Type of Enzyme: Nonspecific Inhibitor (7)
Denaturation,
pH,
temperature,
Acids & bases,
Alcohol,
Heavy Metals,
Reducing Agents
Type of Specific Inhibitors (2)
inhibition can be ________ or __________
- Irreversible Enzyme Inhibitors
- Reversible Enzyme Inhibitors
Certain compounds inhibit enzymes - decrease the rates of their ___________
catalysis
3 types of reversible Inhibitors
The various types of inhibitors can be distinguished by the kinetics of their inhibition.
o competitive inhibitors
o non-competitive inhibitors
o un-competitive inhibitors
suicide inhibitors
Irreversible inhibition
If covalently bond to enzyme, bond relatively easily be ________. i.e. hydrol. of ester
broken
____ Enzyme Inhibition:
is a compound that binds to an enzyme and interferes with its activity. Many drugs are enzyme ___________
Reversible Enzyme Inhibition
inhibitor
The effect of enzyme inhibition:
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.
Irreversible inhibitors
These can be washed out of the solution of enzyme by dialysis.
Reversible inhibitors
The substrate [S] and the inhibitor [I] compete for the same site on the enzyme.
Classical Competitive Inhibition
-
[I] binds to [E] only
In the presence of this inhibition - Km increases,
- Vm remains unchanged or stays the same
Competitive Inhibition
- its inhibitor mimics substrate
- fits into active site
Competitive Inhibition
__________ is a competitive inhibitor of succinate dehydrogenase
- has a structure that is similar to succinate.
- inhibition is reversed by adding succinate
Malonate
The effects of competitive inhibition can be overcome by increasing _________
Substrate [S]
_________ Inhibitor mimic substrate may block active site but may dislodge it.
Competitive Inhibitor
Competition depends upon_________
concentration
Many competitive inhibitors are substrate ___________
analogs (def. chemical compound that resembles substrate)
Benzamidine is an inhibitor of the enzyme ____________
trypsin
Many competitive inhibitors are substrate analogs. Ex.:
An inhibitor of the enzyme Purine Nucleoside Phosphorylase, that utilizes ____________ and is possible drug for the treatment of arthritis
Guanosine
- inhibitor binds to a site other than the active site.
- The effects of this inhibition cannot be overcome by increasing substrate [S]
Non-competitive Inhibition
In the presence of this inhibitor
o Km stays the same
o Vmax decreases
non-competitive inhibitor
A noncompetitive inhibitor has a structure that is different than that of the substrate
o it binds to an ___________ site rather than to the active site
o it distorts the shape of the enzyme, which alters the shape of the active site and prevents the binding of the __________
- allosteric site
- substrate
These are not influenced by the concentration of the substrate. It inhibits by binding irreversibly to the enzyme but not at the active site.
Non-competitive
The effect of enzyme inhibition:
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
Inhibitor binds to a site other than the active site, but only when substrate is bound
Un-competitive inhibition
In the presence of an this inhibitor:
o Km decreases
o Vmax decreases
The effects of this inhibition cannot be overcome by Increasing [S]
Un-competitive inhibition
_____________ enzyme inhibition - Some inhibitors are compounds that form a stable covalent bond with the target enzyme.
Ex. Diisopropyl fluorophosphate (DFP) inactivates _________ proteases by covalently modifying an active site on its residue.
- Irreversible Enzyme Inhibition
- serine proteases
An _________ inhibitor destroys enzyme activity, usually by bonding with side-chain groups in the active site
Irreversible inhibitor
The activity of some enzymes is regulated by reversible _______
ex. pyruvate dehydrogenase
Phosphorylation
- used to control a sequence of reactions
- reaction product may block initial enzyme.
Regulator or feedback
