Food Biochemistry and Food Processing (2 edition)

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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