Biomedical Engineering Reference
In-Depth Information
100
90
80
Trypsin
Cholinesterase
70
60
50
40
30
20
10
0
4
5
6
7
8
9
10
11
12
pH
FIGURE 8.15
The pH-activity profiles of two enzymes.
Theoretical prediction of the pH optimum of enzymes requires a knowledge of the active site
characteristics of enzymes, which are very difficult to obtain. The pH optimum for an enzyme
is usually determined experimentally.
Figure 8.15
depicts variation of enzymatic activity with
pH for two different enzymes.
8.2.5.2. Temperature Effects
The rate of enzyme-catalyzed reactions increases with temperature up to a certain limit.
Above a certain temperature, enzyme activity decreases with temperature because of enzyme
denaturation.
Figure 8.16
depicts the variation of reaction rate with temperature and the pres-
ence of an optimal temperature. The ascending part of
Fig. 8.16
is known as temperature acti-
vation. The rate varies according to the Arrhenius equation in this region.
r
max
¼ k
2
½
E
(8.86)
E
a
RT
k
2
¼ k
20
exp
(8.87)
where E
a
is the activation energy (kJ/mol), and [E] is the active enzyme concentration.
The descending part of
Fig. 8.16
is known as temperature inactivation or thermal denaturation.
The kinetics of thermal denaturation can be expressed as.
d
d
t
¼ k
d
½
½
E
E
(8.88)
e
k
d
t
(8.89)
where [E]
0
is the initial enzyme concentration and k
d
is the denaturation constant. k
d
also
varies with temperature according to the Arrhenius equation.
½
E
¼½
E
0
E
d
RT
k
d
¼ k
d
0
exp
(8.90)
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