Physical Chemistry 3: — Chemical Kinetics — - Christian-Albrechts ...

9.2 Heat explosions 214
10. Catalysis
The net rate of a chemical reaction may be affected by the presence of a third species
even though that species is neither consumed nor produced by the reaction. If the rate
increases, we speak of catalysis. If the rate decreases, we speak of inhibition.
In general, we have to distinguish
• homogeneous catalysis,
• heterogeoues catalysis.
10.1 Kinetics of enzyme catalyzed reactions (homogeneous catalysis)
The mechanism describing the homogeneous catalytical activity of enzymes has first
been elucidated by Michaelis and Menten (1914).
I
Experimental observations on enzyme catalysis:
(1) For constant substrate concentration [S] 0
, the reaction rate is proportional to
the concentration of the enzyme [E] 0
∝ [E] 0
for [S] 0
= const (10.1)
(2) At an applied enzyme concentration [E] 0
,thereactionrate first increases with
increasing substrate concentrations [S] 0
andthenreachessaturation,asisshown
in Fig. 10.1.
I
Figure 10.1: Enzyme catalysis: Michelis-Menten kinetics.