Food Biochemistry and Food Processing

188 Part II: Water, Enzymology, Biotechnology, and Protein Cross-linking

a rectangular hyperbola through the origin with
asymptotes vVmaxand [S] 
Km(Fig. 8.9A).
The term hyperbolic kineticsis also sometimes used
to characterize such kinetics.
There are several available methods for determin-
ing the parameters from the Michaelis-Menten
equation. A better method for determining the val-
ues of Vmax and Km was formulated by Hans
Lineweaver and Dean Burk and is termed the
Lineweaver-Burk (LB) or double reciprocal plot
(Fig. 8.9B). Specifically, it is a plot of 1/vversus
1/[S], according to the equation:

Such a plot yields a straight line with a slope of
Km/Vmax. The intercept on the 1/vaxis is 1/Vmaxand
the intercept on the 1/[S] axis is
1/Km.

111

v

K

VSV

=⋅+m

max [] max

The rate of an enzymatic reaction is also affected

by changes in pH and temperature (Fig. 8.10). When

pH is varied, the velocity of reaction in the presence

of a constant amount of enzyme is typically greatest

over a relatively narrow range of pH. Since enzymes

are proteins, they possess a large number of ionic

groups, which are capable of existing in different

ionic forms. The existence of a fairly narrow pH op-

timum for most enzymes suggests that one particu-

lar ionic form of the enzyme molecule, out of the

many in which it can potentially exist, is the catalyt-

ically active one. The effect of pH changes on vis

reversible, except after exposure to extremes of pH

at which denaturation of the enzyme may occur.

The rate of an enzymatic reaction increases with

increasing temperature. Although there are signifi-

cant variations from one enzyme to another, on aver-

age, for each 10°C rise in temperature, the enzymat-

ic activity is increased by an order of two. After

Table 8.2.(Continued)

Type of
Cofactor Reactions Catalyzed Structure

Nicotinamide adenine Redox reactions
dinucleotide (NAD) (e.g., dehydrogenases)

Heme c Activate substrates