Food Biochemistry and Food Processing

8 Enzyme Engineering and Technology 189

exposure of the enzyme to high temperatures (nor-
mally greater that 65°C), denaturation of the en-
zyme may occur and the enzyme activity decreases.
The Arrhenius equation provides a quantitative de-
scription of the relationship between the rate of an
enzyme-catalyzed reaction (Vmax) and the tempera-
ture (T):

where Eais the activation energy of the reaction, Ris
the gas constant, and Ais a constant relevant to the
nature of the reactant molecules.
The rates of enzymatic reactions are affected by
changes in the concentrations of compounds other

LogV

E

RT

max a A

,

=

−

+

2 303

than the substrate. These modifiers may be activa-

tors (i.e., they may increase the rate of reaction) or

inhibitors (i.e., their presence may inhibit the en-

zyme’s activity). Activators and inhibitors are usual-

ly small molecules or even ions. Enzyme inhibitors

fall into two broad classes: (1) those causing ir-

reversible inactivation of enzymes and (2) those

whose inhibitory effects can be reversed. Inhibitors

of the first class, bind covalently to the enzyme so

that physical methods of separating the two are inef-

fective. Reversible inhibition is characterized by the

existence of equilibrium between enzyme and in-

hibitor (I):

The equilibrium constant of the reaction, Ki,is

given by the equation:

K

ES

i EI

=

[]

[][]

E + I ←⎯⎯⎯→⎯ EI

Figure 8.9.(A) A plot of the initial rate (v)against initial
substrate concentration ([S]) for a reaction obeying the
Michaelis-Menten kinetics. The substrate concentration,
which gives a rate of half the maximum reaction veloci-
ty, is equal to the Km. (B) The Lineweaver-Burk plot.
The intercept on the 1/vaxis is 1/Vmax,the intercept on
the 1/[S] axis is
1/Km,and the slope is Km/Vmax.

Figure 8.10.Relationship of the activity pH and activity

temperature for a putative enzyme.