1
BIOC 440/ Lecture #13 1
“Enzymes II: Kinetics”
I. Enzyme kinetics: why & how?
II. Steady-state kinetics:
Michaelis-Menten eqn.
III. Inhibition of enzyme activity
• ASSIGNED READING: Chap. 6 Section 6.3; Box 6-
2 optional
• Web Resources: “living graphs” in Chapter 6 of
Lehninger Web site (see Bioc440 Schedule page for
link.)
• self-test: see Bioc440 Schedule page for link.
• HOMEWORK PROBLEM SET #5
2
Enzyme Kinetics
Why?
• Measure Reaction RATE via ENZYME ASSAY.
How? S P
(E)
• Study Enzyme & substrate(s) in purified form.
• Measure how rate changes with change in [S], pH, etc.
• Need to be able to monitor [S] or [P] as a function of
time.
3
General form of enzyme-catalyzed rxn: (single substrate rxn)
1. In vivo,
[S] >> [E]. i.e., E is “limiting.”
So, [S] is effectively constant (e sp., early in reaction.)
E + S E · S E + P
k1
k-1
k2
k-2
d[S]/dt=
(k, rate
constants)
4
2. Initial velocity of product formation, “v0”
3. E·S is in “ steady-state.”
E, S, & E·S are in equilibrium.
k2 is SLOW compared to k1 and k-1.
Steady-state means [E·S] does not change w/ time, I.e.,
E + S E · S E + P
k1
k-1
k2
k-2
v0 = d[P]/dt=
