Biologically Modified Carbon Paste Electrodes - Electroanalysis with Carbon Paste Electrodes - page 116

Redox
polymers

Reconstituted
enzyme

Reconstituted
enzyme

Native
enzyme

S

e -

e -

e -

Redox
group

Co-
enzyme

Co-
enzyme

+

+

Polymer

S

Apo-
enzyme

Apo-
enzyme

e -

CNT

AuNP

(A) (B) (C)

FIGURE 5.6 Wiring.of.the.active.center.of.enzymes.with.redox-polymers.(A),.or.by.reconstitution.of.the.
enzyme. from. the. apo-enzyme. with. the. co-enzyme. bound. either. to. carbon. nanotubes,. CNT. (B),. or. to. gold.
nanoparticles,.AuNP.(C).

The. irst. and. the. most. widely. used. oxidase. [73],. and,. in. fact,. the. most. popular. enzyme. of. all.
incorporated. in. CPEs,. has. been. glucose. oxidase.(GOD,. most. frequently.from. Aspergillus niger ),.
either.alone.or.together.with.a.redox.mediator.(Chapter.8,.Table.8.19)..GOD.is.dependent.on.a.lavin.
cofactor.(i.e.,.FAD,.lavin.adenine.dinucleotide).strongly.bound.inside.the.enzyme.structure,.as.for.
all.the.oxidases..The.most.often.utilized.mediators.were.ferrocene.and.its.derivatives,.as.well.as.
quinones.and.benzoquinones.or.HRP.
Beside.GOD,.many.other.oxidases.were.used.to.design.CP-biosensors.(see.Section.8.4.and.the.
respective. tables).. They. include. tyrosinase,. polyphenol. oxidase,. and. laccase,. which. were. widely.
applied.to.the.detection.of.phenolic.and.catechol.compounds,.xanthine.oxidase,.l-.or.d-amino.acid.
oxidase,.alcohol.oxidase,.l-glutamate.oxidase,.pyruvate.oxidase,.cholesterol.oxidase,.pyranose.oxi-
dase,.amine.oxidase,.choline.oxidase,.and.others..These.enzymes.react.similarly.to.GOD,.with.an.
intimately.bound.cofactor,.with.or.without.mediator.(using.molecular.oxygen.as.electron.acceptor.
in.the.latter.case),.and.several.of.them.can.be.used.in.bienzyme.conigurations.

5.2.2.2 Dehydrogenases
Contrarily.to.oxidases,.dehydrogenases.do.not.require.molecular.oxygen.as.electron.acceptor..One.
may. distinguish. two. groups. of. dehydrogenases:. those. with. a. soluble. cofactor. acting. as. a. cosub-
strate.in.the.enzymatic.reaction.(nicotinamide.adenine.dinucleotide.NAD + /NADH.or.nicotinamide.
adenine.dinucleotide.phosphate.NADP + /NADPH).or.bound.cofactors.(lavin.adenine.dinucleotide,.
FAD + /FADH,.or.pyrroloquinoline.quinone).(see.Scheme.5.5).
A.review.surveys.CP-biosensors.based.on.immobilized.dehydrogenases.[156]..Again,.the.litera-
ture.is.surveyed.in.Chapter.8..The.most.widely.used.enzymes.are.alcohol.dehydrogenase.and.those.
related.to.sugar.detection:.glucose.dehydrogenase,.fructose.dehydrogenase,.oligosaccharide.dehy-
drogenase,.aldose.dehydrogenase,.and.pyrroquinoline.quinone.glucose.dehydrogenase.
Other. related. enzymes. include. lactate. and. glutamate. dehydrogenase,. d-gluconate. dehydroge-
nase,.glycerol.dehydrogenase,.and.others..Usually.the.cofactor.NAD(P) + .is.added.as.a.modiier.at.
the.electrode.surface;.the.reoxidation.of.the.reduced.intermediate.NAD(P)H.is.commonly.exploited.
as.a.signal.for.the.substrate;.it.can.be.monitored.directly,.mediated,.or.with.the.aid.of.diaphorase.