Biomedical Engineering Reference
In-Depth Information
antiinflammatory agent; and urokinase is used in dissolving and preventing blood clots.
Asparaginase, which catalyzes the conversion of L -asparagineto L -aspartate, is used as an
anticancer agent. Cancer cells require L -asparagine and are inhibited by asparaginase. Aspar-
aginase is produced by E. coli. Glucose oxidase catalyzes the oxidation of glucose-to-gluconic
acid and hydrogen peroxide, which can easily be detected. Glucose oxidase is used for the
determination of glucose levels in blood and urine. Penicillinases hydrolyze penicillin and
are used to treat allergic reactions against penicillin. Tissue plasminogen activator (TPA)
and streptokinase are used in the dissolution of blood clots (particularly following a heart
attack or stroke).
The development of biosensors using enzymes as integral components is proceeding
rapidly. Two examples of immobilized enzyme electrodes are those used in the determina-
tion of glucose and urea by using glucose oxidase and urease immobilized on the electrode
membrane, respectively. Scarce enzymes (e.g. TPA) are finding increasing uses, as the tech-
niques of genetic engineering now make it possible to produce usable quantities of such
enzymes. The preceding list of enzymes and uses is not exhaustive, but merely illustrative.
8.7. KINETIC APPROXIMATION: WHY MICHAELISeMENTEN
EQUATION WORKS
In Enzyme Kinetics Section, we have discussed the kinetic models of enzyme-catalyzed
reactions via two approximations: 1) rapid equilibrium steps and 2) PSSH. Either approach
lead to an equation that looks similar and when the parameters are lumped, the two equa-
tions become identical. The resulting equation is commonly referred to as Michaelis e Menten
equation. The success or usefulness of this equation cannot be underestimated as it has been
applied to cases where the simple mechanistic model it implies is not nearly close to the real
case. We shall examine why this is the case in this section.
Before we proceed on the discussion, let us consider a simple bioreaction network or
pathway that is illustrated in Fig. 8.18 to be carried out in a batch reactor,
S
þ
E
S $ E
(8.101)
%
S $ E
P $ E
(8.102)
%
P $ E
P
þ
E
(8.103)
%
(8.104)
The uptake of substrate by the enzyme (or substrate e enzyme complexing) is described as
a reversible reaction, i.e.
þÞ ¼
overall
S
% P
r 1 ¼ k 1 C S C E k 1 C SE
(8.105)
The catalytic reaction occurring or assisted by the enzyme is governed by
r 2 ¼ k C C SE k C C PE
(8.106)
and finally, the discharging of product is governed by
r 3 ¼ k 3 C PE k 3 C P C E
(8.107)
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