Corynebacterium glutamicum - JUWEL - Forschungszentrum Jülich

2. Theory
Inhibition
Some catalytic conversions are inhibited by certain substances. Based on the principle
of reversibility of each chemical process at a molecular level, each product also inhibits
its own production.
The catalytic reactions (such as enzymatic reactions) can be inhibited through different
mechanisms such as competitive, non-competitive or uncompetitive inhibition.
Competitive inhibition occurs when the inhibitor and the substrate compete for the
same active site. This can be mathematically described by the following equation:
r = vmax
KS ·
vmax · CS
�
1+ CI
KI
+ CS
KS
� (2.24)
Non-competitive inhibitors bind the catalyst or the catalyst-substrate complex, preventing
the conversion. This can be described by:
r = vmax
vmax · CS
�
KS · 1+ CI
� (2.25)
CS CS·CI
+ + KI KS KS·KI
Uncompetitive inhibitors only bind the catalyst-substrate complex but do not inactivate
the catalyst before binding of the substrate. This can be described by:
r = vmax
vmax · CS
�
KS · 1+ CS
� (2.26)
CS·CI + KS KS·KI
A special case of this form of inhibition is the inhibition of the reaction by excess of
substrate:
r = vmax
vmax · CS
�
KS + CS + C2 � (2.27)
S
KI
This happens when a second substrate molecule can bind the complex and prevent the
conversion.
A more detailed explanation of the shown mechanisms and equations is for instance
shown in Biselli (1992). In many enzymatic processes, the real mechanisms are much
more complex than the shown simple cases and in complete cells, even much more
complex mechanisms take place. These complex regulatory mechanisms are beyond the
scope of the current work and are often not completely understood. Several of the
shown inhibition kinetics have been used for cellular kinetics. Equation 2.27 for instance
corresponds to the well-known Andrews kinetics (Andrews, 1968).
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