Inhibited Enzyme Kinetics

1
Inhibited Enzyme Kinetics

• Inhibitors may bind to enzyme and reduce their
  activity.
• Enzyme inhibition may be reversible or
  irreversible.
• For reversible enzyme inhibition, there are
• -
• -
• -

2
Inhibited Enzyme Kinetics

• Competitive inhibitors (I)
• - substrate analogs
• - compete with substrate for the active site of
  the enzyme

K1
ES
K-1

I
K I
EI
3
Inhibited Enzyme Kinetics

• Competitive inhibitors (I)
• Assume rapid equilibrium and with the
  definitions of

4
Inhibited Enzyme Kinetics

• Competitive inhibitors (I),
• we can obtain,

When I 0,
Remains that of
Michaelis-Menten equation.
is .
5
Inhibited Enzyme Kinetics

• Noncompetitive inhibitors (I)
• - not substrate analogs
• - bind on
  .

Km
ES


I
I
K I
K I
Km
EIS
ESI
6
Inhibited Enzyme Kinetics

• Noncompetitive inhibitors (I)
• Assume
• - rapid equilibrium
• - same equilibrium constants of inhibitor
  binding to E and ES KI
• - same equilibrium constants of substrate
  binding to E and EI

Km
7
Inhibited Enzyme Kinetics

• Noncompetitive inhibitors (I)

8
Inhibited Enzyme Kinetics

• Noncompetitive inhibitors (I)
• we can obtain,

remains in
Michaelis-Menten equation.
is .
When I 0,
9
Inhibited Enzyme Kinetics

• Uncompetitive inhibitors (I)
• - have no affinity for
  itself
• - bind only to the .
• Assume rapid equilibrium,

Km
ES

I
K I
ESI
10
Inhibited Enzyme Kinetics

• Uncompetitive inhibitors (I)

11
Inhibited Enzyme Kinetics

• Uncompetitive inhibitors (I)
• we can obtain,

- in Lineweaver-Burk Plot
12
Inhibited Enzyme Kinetics

• Uncompetitive substrate inhibitors
• - can cause inhibition at substrate
  concentration
• - bind only to the .
• Assume rapid equilibrium,

Km
ES

S
K SI
ES2
13
Substrate Inhibition
14
Inhibited Enzyme Kinetics

• Uncompetitive substrate inhibitors (I)

15
Inhibited Enzyme Kinetics

• Uncompetitive substrate inhibitors (I)
• we can obtain,

At low substrate concentration
ltlt1
Michaelis-Menten Equation
At high substrate concentration
16
Inhibited Enzyme Kinetics

• Uncompetitive substrate inhibitors (I)
• The substrate concentration resulting in the
  maximum reaction rate can be determined by
  setting dv/dS0, Smax is given by

17

• Uncompetitive substrate inhibitors (I)
• Determine Smax

18
Inhibition Estimation

• Product formation rate v S v has a peak?
• If yes, then its substrate inhibition.
• - get Smax from the plot of vs.
• - at low substrate concentration, obtain Vm and
  Km graphically or through direct calculation.
• - calculate KI through
• If no, then examine the data with and without
  inhibitors in 1/v 1/S plot (Lineweaver-Burk
  Plot).

19
Estimation of Inhibited Enzyme Kinetics
20
Estimation of Inhibited Enzyme Kinetics

• Determine the type of inhibition.
• Determine the parameters for Michaelis-Menten
  equation without inhibition.
• Determine the parameter of KI for inhibited
  kinetics.

21
Summary of Inhibited Kinetics

• For reversible enzyme inhibition, there are
• - competitive
• - noncompetitive
• - uncompetitive
• - substrate inhibition
• Determine parameters for all these types of
  inhibition kinetics.