Effect of pH and temperature on enzyme activity notes

Dr.S.Karthikumar
Asst. Prof., Dept. of Biotechnology
Kamaraj College of Engineering and Technology
S.P.G.C.Nagar, Virudhunagar, Tamilnadu, India

1. Effect of pH and Temperature on
Enzyme Activity
Dr.S.Karthikumar
Asst. Prof., Dept. of Biotechnology
Kamaraj College of Engineering and Technology
S.P.G.C.Nagar, Virudhunagar, Tamilnadu, India

2. •EachenzymehasanoptimumpHatwhichitworksbest
•TrypsinandPepsinarebothenzymesinthedigestivesystemwhich
breakproteinchainsinthefoodintosmallerbits
•Pepsinworksinthehighlyacidicconditionsofthestomach.Ithasan
optimumpHofabout1.5.
•Trypsinworksinthesmallintestine,whichhaveoptimumpHofaround8.0
•pHaffectthestructureofanenzymemolecule,andthesortsof
bondsthatitmayformwithitssubstrate

3. If a enzyme has an optimum pH around 7, and
reaction mixture pH is also around 7

4. If pH is more acidic
at a lower pH -in other words under acidic conditions. It won't affect the -NH
3
+
group, but the -
COO
-
will pick up a hydrogen ion
no longer have the ability to form ionic bonds between the substrate and the enzyme

5. If pH is more alkali
the -COO
-
group won't be affected, but the -NH
3
+
group will lose a hydrogen ion

6. •Theratesofenzyme-catalysed
reactionsvarywithpH
•ThepHatwhichtherateisa
maximumiscalledthepH
optimum
•theplotofrateagainstpHis
calledapHprofile

7. Reaction scheme considering the binding of substrate to the protonated and unprotonatedenzyme
Rate limiting step is the dissociation of ES complex (Low Kcat)
Proton transfer is more rapid than that of any other chemical group
4 equilibrium constants = K
S, K
E, K
ES, K
S’

8. •All the 4 equilibrium constants are not independent but are related
K
Ex K
S’ = K
ESx K
S
•If K
E= K
ESthen K
S’ = K
S
There is no difference in the substrate binding between protonated and
unprotonatedenzyme
•If K
Eǂ K
ES
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10. Effect of Temperature on Enzyme Activity
•Formoleculestoreact,theyhavetocollidewithanenergyequaltoorgreaterthan
theactivationenergyforthereaction
•Heatingareactionmakesthemoleculesmovefasterandsocollidemoreoften.
Morecollisionsinagiventimemeansafasterreaction.
•Heatinganenzymegivestheproteinchainsextraenergyandmakesthemmove
more.Iftheymoveenough,thenthebondsholdingthetertiarystructureinplace
willcomeunderincreasingstrain.
•Hence,reactiontemperatureinfluencestheReactionRate
•Butabovecertainpointoftemperaturethereisadramaticfallinreactionrate.
•Athighertemperature,theweakerbondswillbreakfirst-vanderWaalsattractions
betweensidegroups,andthenhydrogenbonds.Assoonasthesebondsholdingthe
tertiarystructuretogetherarebroken,thentheshapeoftheactivesiteislikelyto
belost.

11. •Thetemperatureatwhichtherate
isfastestiscalledtheoptimum
temperatureforthatenzyme.
•Differentenzymeshavedifferent
optimumtemperatures.
•Theoptimumtemperaturefora
particularenzymevariesdepending
onhowlongitisexposedtothe
highertemperatures

12. •Arrhenius equation is the starting point to relate temperature and
reaction rate

15. THANK YOU