Food Biochemistry and Food Processing (2 edition)

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BLBS102-c07 BLBS102-Simpson March 21, 2012 11:12 Trim: 276mm X 219mm Printer Name: Yet to Come


7 Biocatalysis, Enzyme Engineering and Biotechnology 137

Table 7.3.The Characteristic of Each Type of Inhibition and Their Effect on the Kinetic ParametersKmandVmax

Inhibitor Type Binding Site on Enzyme Kinetic Effect

Competitive Inhibitor The inhibitor specifically binds at the
enzyme’s catalytic site, where it competes
with substrate for binding:

E ES E + P

+S
-S →
I
–I
EI

Kmis increased;Vmaxis unchanged.
LB equation:
1
v

=

Km
Vmax

(
1 +

[I]
Ki

)
1
[S]

+

1
Vmax
Non-competitive Inhibitor The inhibitor binds to E or to the ES
complex (may form an ESI complex) at a
site other than the catalytic. Substrate
binding is unchanged, whereas ESI
complex cannot form products.

E +S-S ES → E + P

ES E + P

+S
-S

I
–I

I
–I
EI

Kmis unchanged;Vmaxis decreased proportionately
to inhibitor concentration.
LB equation:
1
v

=

Km
Vmax

·

(
1 +

[I]
Ki

)
·

1
[S]

+

1
Vmax

(
1 +

[I]
Ki

)

Uncompetitive Inhibitor Binds only to ES complexes at a site other
than the catalytic site. Substrate binding
alters enzyme structure, making
inhibitor-binding site available:

EIS

E +S-S ES → E + P
I
–I

KmandVmaxare decreased.
LB equation:
1
v

=

Km
Vmax

·

1
[S]

+

1
Vmax

(
1 +

[I]
Ki

)

can refer bothFandGas ‘free energy’ (Finkelstein and Ptitsyn
2002). Eventually, when we study the thermodynamic behaviour
of an enzyme, regarding its structural stability or its functionality,
we have to do with Gibb’s free energy (G), entropy (S)and
enthalpy (H).
As far as experimental procedures are concerned, someone
can use two equations in order to measure the thermodynamic

parameters, applying temperature differentiation experimental
protocols (Kotzia and Labrou 2005). These equations are the
Arrhenius (Equation 4) and the Eyring equations, which basi-
cally describe the temperature dependence of reaction state. So,
considering an enzymic reaction as a chemical reaction, which
is characterised by a transition state, we can efficiently use the
Eyring’s equation. This equation is based on transition state
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