Lecture 11 - Enzyme Rate (Michaelis-Menten vs Allosteric Enzymes) Flashcards
Enzymes catalyse thermodynamically favourable
reactions by
lowering the activation energy.
To model of enzyme catalysis, we use a very simple system in which an
enzyme, E, converts a single substrate, S, to a single product, P, that is instantly released.
is the conversion of enzyme, E, converts a single substrate, S, to a single product, P, that is instantly released reversible or irreversible?
irreversible
Relative speeds of k1 and k-1 define
how tightly
substrate binds.
The rate of catalysis, k2, relates to
energy of activation for the transition state.
‘Steady state’ refers to
time during which [ES] does not change.
why is ES complex necessary for reaction?
so [ES] at any time will govern the rate.
‘progress curve’ measures
appearance of product (or disappearance of substrate) with time at steady state.
Following the progress of an enzyme catalysed reaction
we measure…
initial reaction velocity (rate) i.e.
near time zero – symbol is V0
(or Vi or Vinit).
What is The effect of enzyme concentration on reaction rate when there is sufficient excess of substrate?
amount of enzyme increased, the rate of reaction increases.
when substrate is in excess what is proportional to [E] enzyme concentration?
Vo, initial velocity,
As [S], concentration of substrate, is increased, the initial rate V0…
increases in a linear way at first.
what does the hyperbolic curve show on V0 vs [S] graph?
Enzyme properties.
initial rate (V0) increase linear
Enzyme actives sites are occupied. rate of reaction stops increasing.
what can be identified on a V vs [S] curve?
Two kinetic parameters
Vmax
maximum velocity possible,
when [S] = ∞.
Km
Michaelis constant
substrate concentration at which Vobs = Vmax /2.
The Vobs vs. [S] curve is described by
Michaelis-Menten equation:
Michaelis-Menten equation:
Vobs = Vmax [S] / Km + [S]
How to determine enzyme kinetic parameters?
Michaelis-Menten behaviour
Michaelis-Menten model and assumptions
- Product is not converted back to substrate.
- Haldane’s steady state assumption: the rate of ES
formation equals the rate of its breakdown; that is
d[ES] / dt = 0
- Measuring initial rate ensures [S] does not change
significantly (and [S] is much greater than [E]).
Michaelis-Menten model and assumptions
what is Haldane’s steady state assumption?
d[ES] / dt = 0
Haldane’s steady state assumption: the rate of ES
formation equals the rate of its breakdown;
ES complex converts to E + P with
first order kinetics
Single molecule events, like radioactive decay, occur with a set probability, giving
first order kinetics.
why will ES ® E + P step follow 1st order kinetics?
If each ES complex has the
same chance of going
through the transition state,