Biomedical Engineering Reference
In-Depth Information
PyOD catalyzes the consumption of pyruvate and phosphate in the presence of oxygen, while
hydrogen peroxide, carbon dioxide, and acetyl phosphate are generated. This reaction is shown
below (14.17):
PyOD
Pyruvate
+
phosphate
+
O
2
acetyl phosphate
+
H
2
O
+
CO
2
(14.17)
Based on Reaction 14.18, PyOD can be used to prepare biosensors for the direct detection of
pyruvate [82] and phosphate [83]. PyOD is also involved in the biosensing detection of alanine with
the assistance of other reactions including a dehydrogenation process catalyzed by alanine dehydro-
genase (AlaDH, E.C. 1.4.1.1) (14.18) and a hydroxidation process catalyzed by salicylate hydroxylase
(SHL, E.C.1.14.13.1) (14.19) [84].
ALaDH
NAD
+
Alanine
+
pyruvate
+
NADH
(14.18)
SHL
NAD
+
Salicylate
+
NADH
+
O
2
catechol
+
+
CO
2
(14.19)
14.1.1.7 Glutamate Oxidase
GLOD (E.C. 1.4.3.11) from
Streptomyces
is an extracellular heterotrimeric enzyme consisting
of α, β, and γ subunits of molecular masses equal to 39, 19, and 16 kDa, respectively [85]. This
enzyme specifi cally catalyzes the oxidative deamination of glutamate in the presence of water
and oxygen with the formation of ketoglutarate, ammonia, and hydrogen peroxide as in Reaction
14.20. GLOD has excellent potential as the principal component in the biosensing determination
of glutamate [86,87]:
GOLD
Glutamate
+
O
2
+
H
2
O
ketoglutarate
+
H
2
O
2
+
NH
3
(14.20)
14.1.2 M
ICROORGANISMS
Microbial biosensors are an important category of biosensors, which use microorganisms as
biological transducers. Based on the action mechanism, microbial biosensors can be divided into
two kinds: electrochemical microbial biosensor and bioluminescent microbial biosensor. The
electrochemical microbial biosensor is classifi ed into respiratory activity detection biosensor and
electrode activity detection biosensor. Biochemical oxygen demand (BOD) biosensor that belongs to
the respiratory activity detection biosensor is a superior kind of biosensor. BOD is a commonly used
environmental index showing the amount of oxygen that microbes require to decompose organic
materials in a given wastewater sample.
In comparison with the enzymes used in biosensor, microorganisms can be easily manipulated
and adapted to consume and degrade new substrate under certain cultivatable conditions [88-90].
Additionally, the progress in molecular biology or recombinant DNA technology has opened endless
possibilities of tailoring microorganisms to improve the activity of an existing enzyme or express
foreign enzyme or protein in host cell [91,92]. All these factors make microorganisms excellent
biological transducers to construct biosensors [93].
Till date, there are mainly two categories of microorganisms used in the preparation of biosen-
sors, bacterium (including
E. coli,
Bacillus subtilis,
Bacillus licheniformis
, and so on) and yeast
(including
Tr ich osporon cu ta neu m ,
Saccharomyces cerevisiae,
Arxula adeninivorans
, and so on).
These microorganisms used in biosensors are introduced in detail as follows.
