Enzyme Kinetics I
Biological Catalysts
• enzyme-catalysed reaction
– reaction rate
depends on [S]
Initial Velocity or V0
– rate affected
– equilibrium never affected
Substrate concentration or [S]
Michaelis-Menten equation
• enzymes combines reversibly with substrate
– form ES complex.
• ES complex breaks downs substrate yielding free
enzyme and product
– rate limiting step
E+S
ES
E+P
Michaelis-Menten equation
Initial Velocity or V0
Michaelis-Menten equation
Vmax [ S ]
Vo 
Km  [ S ]
Substrate concentration or [S]
Linear Plots
double-reciprocal plot or Lineweaver-Burk plot
1
V0
Slope  Km
1
Vmax
1
1
[S ]
Km
Vmax
1 Km  [ S ]

V0
Vmax [ S ]
Velocity
(umol/min)
[S]
(M)
Velocity
(1/umol/min)
[S]
(1/M)
130
6.5 * 10-4
0.00769
1.539 * 103
116
2.3 * 10-4
0.00862
4.35 * 103
87
7.9 * 10-5
0.0115
1.27 * 104
63
3.9 * 10-5
0.0159
2.56 * 104
30
1.3 * 10-5
0.0330
7.69 * 104
10
3.7 * 10-6
0.1000
2.7 * 105
Reciprocal
data
0.12000
y = 3E-07x + 0.0071
0.10000
0.08000
0.06000
0.04000
0.02000
0.00000
-50000.0
0.0
50000.0
100000.0
150000.0
200000.0
250000.0
300000.0
Reversible Inhibition
• Competitive inhibition
– Inhibitor competes with the substrate for the active
site of an enzyme
1
V0
[I]
1
Vmax
1
[S ]
• Uncompetitive inhibition
– Inhibitor binds at a site distinct from the substrate
active site AND only to ES complex
1
V0
[I]
1
[S ]
• Mixed inhibition
– Inhibitor binds at a site distinct from the substrate
active site AND either E or ES
1
V0
[I]
1
[S ]