Enzyme Kinetics Notes for Chem 527
k1
S
P
k-11
First Order Kinetics
velocity or v = d[P]/dt = -d[S]/dt
v = k1 [S], where k1 has units of sec-1
Second Order Kinetics
v = k [S1][S2]
where k has 2nd order units of M-1sec-1
Rate Constant
k = Қ T/Һ exp{-Ea/RT}
R = 1.987
1 987 call moll-11K-11
Һ = 6.626075 x 10-34 J S, which is Planck’s constant
Қ = 1.38066 x 10-23 J K-1, which is the Boltzmann constant
T is in Kelvin
gy in cal mol-1
Ea is activation energy
1
Steady State
Assumption
E+S
k1
k-1
ES
k2
k-2
EP
k3
k-3
E+P
1) Steady State Conditions d[ES]/dt = 0
2) Initial velocity = v0 = Vmax [S]/( KM + [S]), this is the
Michaelis-Menton Equation
at saturating conditions and under initial velocity
conditions, [S] > 10 x KM
Vmax = k2 [ES] and the units are μmol L-1 sec-1
For simple mechanisms k2 = kcat (assuming k3 >> k2)
kcat, which is corrected for [enzyme], is called the pseudo
first order rate constant (units of sec-1).
The enzyme activity is
proportional to the [enzyme]
2
2x-substrate
For ADH
this will
be [NADH]
Follow reaction by appearance of NADH ε340 = 6,220 M-1 cm-1
The enzyme saturation curve
Michaelis-Menton Equation
v =
Vmax [S]
KM + [S]
3
Lineweaver-Burk Replot of Saturation Curve
4
Competitive Inhibition
5