Biomedical Engineering Reference
In-Depth Information
either.carbon-based.or.inorganic.nanoparticles..Palocci.et.al..(2007).immobilized.lipases.
from.
Candida rugosa
. and.
Pseudomonas cepacia
. on. polymethylmethacrylate. (PMMA).
and. polystyrene. (PS). nanoparticles.. They. were. able. to. achieve. stable,. non-covalent.
adsorption. on. nanoparticles. ranging. from. 100. to. 300.nm. in. diameter.. Adsorption. was.
rapid,. with. enzyme. loadings. as. high. as. 100.mg. enzyme/mg. of. support.. Greater. than.
70%.of.the.activity.was.retained.when.the.lipases.were.adsorbed.onto.nanostructured.
PS,. in. contrast. with. ∼30%. activity. upon. adsorption. onto. amorphous. PS. or. PMMA..
A. signiicant. increase. in. activity. compared. with. free. enzyme. was. observed. when. the.
lipase-NP. complexes. were. used. for. transesteriication. reactions. in. hexane. or.
t
-buthyl-
methyl-ether.. In. order. to. provide. covalent. immobilization. with. controlled. attachment.
orientation.(reducing.activity.losses),.Wong.and.coworkers.prepared.coenzyme.A.(CoA)-
derivatized. PS. NPs.. They. then. employed. a. phosphopantetheinyl. transferase-enzyme.
(Sfp). to. catalyze. the. immobilization. of. recombinant. proteins. bearing. the. small. (11.
amino.acid.residues).“ybbR”.tag.(Wong.et.al..2010)..They.immobilized.both.the.model.
protein. thioredoxin. (Trx). and. two. biocatalytically. interesting. proteins,. arylmalonate.
decarboxylase.(AMDase).enzyme.from.
Bordetella bronchiseptica
.and.glutamate.racemase.
(GluR).from.
Aquifex pyroilus
..While.the.engineered.ybbR.tag.actually.improved.catalytic.
eficiency,.particularly.for.the.glutamate.racemase,.the.immobilized.enzymes.displayed.
a.lower.eficiency.compared.to.their.counterparts.in.solution..The.authors.attributed.this.
reduction.in.eficiency.to.the.electrostatic.repulsion.of.the.negatively.charged.substrate.
attempting.to.approach.the.NPs.that.were.also.negatively.charged.due.to.the.unreacted.
surface.carboxylates.
In. two. somewhat. unusual. reports,. polyethyleneimine. (PEI). and. the. R5. peptide.
(H2N-SSKKSGSYSGSKGSKRRIL-COOH). were. used. as. nucleation. catalysts. to. create.
silicate. nanoparticles. with. enzymes. immobilized. either. on. the. surface. or. in. the. silicate.
structures.(He.et.al..2008;.Neville.et.al..2011)..He.and.coworkers.reported.a.microluidic.
reactor.in.which.they.synthesized.glucose.oxidase.(GOD).functionalized.silica.nanopar-
ticles.using.2000-MW.PEI.or.R5.as.a.catalyst..By.optimizing.the.amount.of.PEI.added.to.the.
system,.they.obtained.∼90%.immobilization.of.the.GOD..The.enzyme.immobilized.in.this.
manner.showed.good.stability.although.there.was.a.general.loss.of.activity.upon.immo-
bilization..The.high.level.of.immobilization.using.PEI.can.be.attributed.to.the.electrostatic.
interaction.between.the.PEI.and.GOD;.however,.this.interaction.also.limits.the.mobility.of.
the. immobilized. enzymes,. producing. orientation. hindrance. of. the. enzyme's. active. sites.
compared.to.GOD.in.solution..In.contrast,.using.R5.as.the.catalyst.for.nucleation.gave.a.
much. lower. immobilization. eficiency;. however,. the. GOD. immobilized. using. R5. in. the.
microluidic.reactor.exhibits.a.similar.K
m
.value.and.k
cat
.value.(16.mM,.22.s
−1
).to.free.GOD.
(13.mM,.20.s
−1
),.indicating.that.there.is.little.hindrance.of.the.immobilized.enzyme.active.
sites..They.attribute.the.difference.in.behavior.to.an.absence.of.electrostatic.interactions.
between.the.GOD.and.the.R5..In.the.case.of.the.R5.immobilization,.the.enzymes.appear.
to. be. physically. entrapped. within. the. mesoporous. silica. nanoparticles,. which. in. turn.
provides. the. enzymes. with. greater. mobility. within. the. pores,. reducing. the. orientation.
hindrance.of.the.enzyme.active.sites. and.enhancing.the.availability.of.the.immobilized.
enzymes.
Bridging.the.worlds.of.surface.immobilization.on.silica.nanoparticles.with.encapsulation,.
Jang.et.al..(2010).covalently.immobilized.GOD.on.the.surface.of.silica.nanoparticles.(SNPs).
using. 3-aminopropyltriethoxysilane. (APTES). followed. by. glutaraldehyde. cross-linking..
The. enzyme-NP. complexes. were. then. entrapped. within. photopolymerized. hydrogels.
prepared.from.two.different.molecular.weights.(575.and.8000.Da).of.poly(ethylene.glycol).
