Biologically Modified Carbon Paste Electrodes - Electroanalysis with Carbon Paste Electrodes - page 118

Lineweaver-Burk Hanes-Woolf Eadie-Hofstee

— 1
i

[ S ]
i

—-

i

i max

Slope
K M

1
K M

- —-— -

-

K M

K M
i max

—- 1
i max

—-—

— 1
[ S ]

— i
[ S ]

[ S ]

FIGURE 5.7 Usual. evaluation. procedures. for. evaluating. the. apparent. Michaelis-Menten. constant. with.
enzyme.electrodes.

5.2.2.5 Enzyme Kinetics
Enzyme.kinetics.are.usually.described.by.the.Michaelis-Menten.model..In.a.simpliied.form.the.
enzyme,. E ,.forms.a.complex.with.the.substrate,. S ,.yielding. ES ,.which.is.followed.by.the.conversion.
to.the.product.and.the.dissociation.of.the.product-enzyme.complex,. EP ..In.case.the.enzyme.con-
centration.and.the.enzyme-substrate.complex.(steady.state).do.not.change.with.time,.the.reaction.
rate,. v ,. tends. to. approach. a. maximum. value,. v max ,. with. increasing. substrate. concentrations.. The.
Michaelis-Menten constant ,. K M ,.corresponds.then.to.the.substrate.concentration,.where.half.of.the.
maximum.reaction.rate.is.attained.(see.Equation.5.1).

⋅ [ ]
+ [ ] .

v S

max

(5.1)

v =

K S

M

.

In.order.to.estimate.the. apparent Michaelis-Menten constant .with.respect.to.the.situation.present.
at. the. electrode. surface,. the. usual. evaluation. procedures. are. applied,. that. is,. Lineweaver-Burk ,.
Hanes-Woolf ,.and. Eadie-Hofstee plots .(Figure.5.7)..Instead.of.reaction.rates,.the.signals.obtained.
for.the.substrate,.that.is,.the.corresponding.currents,.are.used.for.the.approach.

5.2.3 n uCleiC a Cids
Within. the. past. 20. years,. numerous. publications. have. appeared. that. deal. with. carbon. paste.
electrodes.modiied.with.nucleic.acids,.oligonucleotides,.and.base.constituents.of.nucleic.acids..
Deoxyribonucleic.acid,.DNA,.the.main.center.of.research,.shows.high.afinity.toward.carbon.
paste.and.strongly.adsorbs.to.its.surface..DNA.yields.a.signal.below.+1.0.V.vs..SCE.due.to.the.
oxidation.of.guanine;.adenine.moieties.being.also.oxidized.at.slightly.more.positive.potentials..
In. fact,. the. other. bases. typically. produce. oxidation. currents. at. even. higher. potentials. (see.
Figure.5.8).
Studies.of.nucleic.acids.with.carbon.paste.electrodes.may.be.mainly.categorized.into.three.topics.
(see.Section.8.4,.Table.8.23):

. (i). Preconcentration of nucleic acids .with.anodic.stripping.voltammetry;.as.the.accumulation.
is.not.speciic,.different.types.of.DNA.cannot.be.discriminated.
. (ii). Accumulation and interaction studies . with. DNA. as. modiiers;. many. substrates. show.
high.afinity.toward.DNA.and.can.be.accumulated;.the.process.is.often.intercalation.of.
the.target.species.into.the.DNA,.frequently.into.the.minor.groove.of.the.double.helix..
Interaction. studies. include. also. investigations. on. damaging. effects. of. the. substrate. on.
the.modiier.