51144635 factors affecting enzyme activity

8/18/2019 51144635 Factors Affecting Enzyme Activity

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FactorsFactors Affecting Affecting

EnzymeEnzyme Activity Activity


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Enzymes are largeEnzymes are large

globular proteins…globular proteins…• They have a precise 3-D

shape• Some have quaternary

structure• The ‘active site’ (blue)

represents a tiny part ofthe molecule

RuBisCo


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A reminder about A reminder about

protein structure protein structure

Amylase

• Protein structure isachieve by the precisefol in! of secon arystructures to form atertiary structure hel

to!ether by a ran!e of bon types bet"een #-!roups (or ‘si e-chains’)


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Some reaction kinetics…Some reaction kinetics…


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Some reaction kinetics…Some reaction kinetics…


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The ‘Lock and ey!The ‘Lock and ey!

analogy analogy


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The ‘Lock and ey!The ‘Lock and ey!

analogy analogy


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"nduced fit "nduced fit


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Enzymes andEnzymes andtemperature# a tale of t$otemperature# a tale of t$o

effectseffects

Temperature $ o%

%ollision rate ofen&ymes ansubstrates

'umber ofen&ymes remainin!un enature

#eactio


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Enzymes and temperatureEnzymes and temperature

Temperature $ o%

ncreasin! ineticener!y increases

successful

collision rate

#eactio


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Temperature $ o%

Permanent isruptionof tertiary structure

lea s to loss of activesite shape* loss of

bin in! efficiency anactivity

#eactio


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Temperature $ o%

+ptimum temperature

#eactio


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Enzymes and p%Enzymes and p%

• The precise shape of an en&yme (an hence itsactive site ) epen s on the tertiary structure of

the protein• Tertiary structure is hel to!ether by "ea bon s (inclu in! hy ro!en bon s ) bet"een #-!roups (or ‘si e-chains’)

• %han!in! p, can cause these si e chains toionise resultin! in the loss of ,-bon in!


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p,#eactio

.ither si e of the optimum p,* the !ra ual ionisin! ofthe si e-chains (#-!roups)results in loss of ,-

bon in!* 3 o structure*active site shape loss of

bin in! efficiency aneventually en&yme activity

+ptimum p,


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p,#eactio

This loss of activity is onlytruly enaturation atextreme pH since bet"eenoptimum an thesee/tremes* the loss ofactivity is reversible

+ptimum p,


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Enzymes and &S'Enzymes and &S'

0S1

(nitial reactio

arbitrary units

2s soon as a reaction be!ins*0S1 be!ins to fall an so it isimportant that initialreaction rates are measure


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0S1

(nitial reactio

arbitrary units


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0S1

(nitial reactio

arbitrary units

ncreasin! 0S1increases collisionrate an increasesreaction rate


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0S1

(nitial reactio

arbitrary units

All active sites areoccupied .n&ymesare "or in! atma/imum rate

2ll active sitesare not occupie


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Enzymes and &enzyme'Enzymes and &enzyme'

0.n&yme1

(nitial reactio

arbitrary units

%an "e e/plain this in terms ofthe proportions of active sites

occupie 6

7hat factor islimiting here6


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Enzymes and inhibitorsEnzymes and inhibitors

• nhibitors are molecules that preventen&ymes reachin! their ma/imum turnover

numbers• Some inhibitors compete "ith the substrate

for the active site•

Some inhibitors affect the active site shape by bin in! to the en&yme else"here on theen&yme

2ctive site irecte inhibition

'on-active site irecte inhibition


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Active site directed Active site directedinhibitioninhibition

• nhibitor resembles the substrate enou!h to bin to active site an so prevent the bin in! of the substrate8

Substrate

nhibitor

.n&yme


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Active site directed Active site directedinhibitioninhibition

• nhibitor resembles the substrate enou!h to bin to active site an so prevent the bin in! of the substrate8

Substrate

.n&yme$ nhibitorcom le/

.n&ymeactivity is lost


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Enzymes and active site directedEnzymes and active site directedinhibitioninhibition

0S1

(nitial reactio

arbitrary units

2t lo" 0S1* the en&yme is moreli ely to bin to the inhibitor anso activity is mar e ly re uce

Uninhibited

Inhibited


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0S1

(nitial reactio

arbitrary units

2s 0S1 rises* the en&yme isincreasin!ly li ely to bin to the

substrate an so activity increases

Uninhibited

Inhibited


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0S1

(nitial reactio

arbitrary units

2t hi!h 0S1* the en&yme is veryunli ely to bin to the inhibitor an so

ma/imum turnover is achieve

Uninhibited

Inhibited


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(on)active site directed(on)active site directedinhibitioninhibition

• nhibitor oes not resemble the substratean bin s to the en&yme isruptin! theactive site

Substrate

nhibitor

.n&yme


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Substrate

.n&yme

2ctive site ischan!eirreversibility


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Substrate

.n&yme

2ctivity is permanentlylost


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51144635 factors affecting enzyme activity

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