Enzymes as drug targets Flashcards
Enzymes
protein molecules, catalyse a specific reaction, unchanged by the reactions they catalyse
how does enzyme work as catalyst?
providing an alternative pathway for the reaction in which the rate-determining step has a lower Gibbs activation energy than that of the non-catalysed reaction
steps in enzyme kinetics;
1) reversible
2) irreversible
What is The Michaelis Menten Equations?
( π [π¬πΊ])/π π=k1 [E] [S] β(k2 - k-1 )[ES]=0
[E]0 = [ES] + [E]
π½ (ππππ ππ ππππππππ)= ( π½πππ [πΊ])/(π²π΄+[πΊ])
[S] is effectively constant
Define Vmax or (rate)max
maximum velocity the reaction can achieve. It is equal to K2[E]0
What is Km?
the Michaelis constant. It is (k2 +k-1)/k1
The velocity (rate) of an enzyme catalysed reaction increases in a __________ fashion
non-linear
When [S] is large, [S]
> > Km
Maximal Velocity Vmax
π½ (ππππ ππ ππππππππ)= ( π½πππ [πΊ])/([πΊ]) = Vmax = K2 [E]0
[s] cancel each other
What is the turnover number?
number of substrate molecules converted into product by an enzyme molecule in a unit time when the enzyme is fully saturated with substrate
what is the connection between the Vmax and k2?
Vmax and is equivalent to the rate constant k2.
turnover number equation?
K2 = Vmax/[E]0 (s-1)
turnover numbers of most enzymes with their physiological substrates fall in the range from:
1 to 10^4 s-1
KM gives an indication of how _______ the enzyme binds its substrate
tightly
Weak substrate, large KM
high [S] is needed to achieve Vmax/2 (and even more to reach Vmax!)
Good substrate, low KM:
Only a low [S] needed to reach Vmax.
Enzymes as drug targets - altered metabolic pathway
excess or deficiency of a specific metabolite.
Irreversible enzyme inhibitors: what type of bonding?
bind covalently to an enzyme,
or form a highly stable non-covalent association (tight-binding inhibitors)
name an Irreversible enzyme inhibitor?
Penicillins: irreversible enzyme inhibitors specific for a bacterial enzyme (peptidoglycan transpeptidase), needed to build the bacterial wall
name an Irreversible enzyme inhibitor?
Penicillins: irreversible enzyme inhibitors specific for a bacterial enzyme (peptidoglycan transpeptidase), needed to build the bacterial wall
Suicide inactivators or mechanism-based inactivators:
irreversible inhibitors (covalent): one drug molecule completely inactivates one enzyme molecule, and it is lost in the process
How to make inhibitors MORE selective for target? LESS side effects
1) Initially binds reversibly (Intermolecular bonding interactions), then if molecule is held long enough ο irreversible interactions take place
2) use mildly reactive electrophilic groups
Irreversible enzyme inhibitors - strength
EFFECTED by; drug concentration and time after administration we measure the enzyme activity (βhow quickly can the drug inhibit the enzyme)
Reaction of kinetics = step by step?
ADD increasing inhibitor concentrations.
- as [inhibitor] increases, the maximum amount of product formed decreases;
- as [inhibitor] increases, the inactivation rate increases
(curve of P formation drops off faster) - time passes, more enzyme molecules have been inactivated (greater deviation from uninhibited reaction)
> > > > >
good irreversible inhibitor must be specific and inactivate the enzyme rapidly
