Regulation of enzymes Introduction andProperties of Enzymes Enzymes are characteristics to facilitate the Enzymecatalyzed reactions take place Reactants need to pass over the energy barrier Catalys ID: 953327
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Unit-III Enzymes Regulation of enzymes Introduction andProperties of Enzymes Enzymes are char
acteristics to facilitate the Enzyme-catalyzed reactions take place Reactants need to pass o
ver the energy barrier, Catalysts reduce the activation energy activation energy. Toxicityof
the biological systemsChemical reactions in living systems are quite different from that in
the industrial Enzyme-catalyzed reactions have the following characteristics in comparison w
ith the general catalyzed reactions:common features: 2 do and 2 dont&
#148;: no changes in quantity and quality Do not change the unique features: 3 high
8;Enzyme-catalyzed reactions have very high catalytic efficiencyEnzymes have a high degree of
specificity in response to the external ClassificationOxidoreductasesTransferasesHydrolases
LysasesIsomerasesLigases ConventionalNomenclaturesuffixsubstrates(urease)suffixdescriptiveter
mforreactionstheycatalyze(glutematedehydrogenase)Forhistoric(trypsin,amylase)aftergenes(Rec I
nternationalBiochemistrymaintainsclassificationCategorizeaccordinggeneralorganicreactionscata
lyzednumber,systematicshortercommonenzymeSystematic Nomenclature Unlike conventional catalyst
s, enzymes demonstrate the ability to distinguish different substrates. specificities. su
bstrate and implement their catalytic OC NH2 NH2 + H2O + COurease NH NH2 + H2O methyl urea
Relativespecificity protein kinase Aprotein kinase Cprotein kinase G To phopharylate the -OH
group of serine and threonine in the substrate proteins, leading to the activation of protein
s. Lactate dehydrogenase can recognize only the L-form HC H3C COOH H H3C COOH ABCABC Enzyme-
catalyzed reactions can be regulated in response to the external stimuli, satisfying the need
s of biological processes. Regulations can be accomplished through varying the , adjusting t
he , or changing the substrate concentration. Components of Enzymes Almost all the enzymes
are Some functional groups are Lysozymedifferent parts of the polypeptide chain . Two essen
tial groups + Catalytic groupactive center Active centers consists of only one peptide chainC
onjugated enzymes: holoenzyme = apoenzyme + cofactor(protein)(non-protein)Cofactors: me
tal ions; small organic molecules butloosely bound. Often found in metal-Particularly in the
active center, transfer substrates, stabilize enzyme Small sizeTransferringVitamin-like Tig
htly bind through either Remained Mechanism of Enzyme-Catalyzed Reactions Both E and S are r
igid and fixed, so they must be Induced-fit modelThe binding induces conformational changes
of both E and S, forcing them to get a perfect Induced structural changes Kinetics of Enzyme
-Catalyzed Reactions initial k3k1k2ES E+PE+S = rate constant for ES formation
= rate constant for ES dissociation= rate constant for the product k3k1k2ES E+PE+S The mathe
matical expression of the [S] [E], changes of [S] is negligible. Steady-sta
te: the rate of E-S complex disassociation (backward E + S and Describing a hyperboliccurve.
Kmis a characteristic constant of E [S] Km v [S][S] Km v Vmax Vmax =VKm+[S
][S] [S]max First order withrespect to [S]Zero order withrespect to [S] one-half of its maxim
umvelocityelocitydetermined by the structure of E, the substrateand environmental conditions
(pH, T, ionic strength, ) 0Vmax V0 max Km The value of affinity of . The larger the th
e smaller the affinity =Kmk1k3k2+ The reaction velocity of an enzymatic Substrate concentrat
ionEnzyme concentrationTemperatureH Inhibitionof Enzyme Inhibitors are certain molecul
es that can decrease the catalytic rate of an enzyme-catalyzed reaction. Inhibitors ca
n be normalbody metabolites and foreign (drugs and toxins). Inhibitors The inhibition process
can be either The inhibition can be typebinding targetKmVmaxCompetitiveE only=Noncompetitiv
eE or ES=UncompetitiveES onlySummary of inhibition Metal ionscatalytic power. Cofactors Activ
ator ions(loosely bound)Prosthetic Essential ionsCoenzymes Cofactors Essential ionsActi
vator ions: loosely and reversibly bound, often participate in the binding of substrates.
49;Metal ions of metalloenzymes: tightly bound, and frequently participate directly Transfer
electronKeep conformation of E-S complex Neutralize anion CosubstratesProsthetic groups The
Their different enzyme-catalyzed reactions. Supply the AA residues. Can be either apoenzy
mes or through many Remained RegulationEnzyme Manybiologicalprocessestakelocationcatalyticca
pacityproductenzymeconcentrationintrinsiccatalyticefficiency.keystepprocessregulateenzymatice
nzymequantity ReasonsforregulationMaintenanceorderedfashionwastingresourcesConservationenergy
consumejustnutrientsadjustmentresponseenvironmentalchanges control more efficient. rate set b
y an enzyme will dictate the whole pathway, namely, the slowest one or the RegulationEnzymeZ
ymogenactivationAllostericregulationCovalentmodification ClinicalApplications Fundamentalenzy
mespresenthaveSynthesizedliverentercirculation.Impairmentlivergeneticdisorderfall enzymestota
llyabsentconcentrationturnoverintracellularenzymesarereleasedintostream.organdamagedmayelevat
eenzymes Isoenzymegroupenzymesthatcatalyzereactiondifferfromstructure,substrateaffinity,maxre
gulatoryproperties.genedifferentiationdifferentgeneproductsdifferentpeptidesgenePresentdiffer
entsystem,subcellularcomponents(e.g)LactatedehydrogenaseCreatine DiagnosticApplicationsUseful
ness:EnzymeassaysprovideimportantinformationconcerningpresenceseverityProvidemonitoringpatien
tresponseapproaches:enzymaticdirectlyagentsmonitorpresencesubstrates Acute pancreatitisLiver
diseases (hepatitis)Heart attack (myocardial infarction)Cancer of prostate glandLactate deh
ydrogenase (LDH)Heart attack, liver diseasesAlcoholismHepatitisMuscular dystrophyEnzymes for
disease diagnosis TherapeuticApplicationsSuccessfultherapeuticSteptokinase:treatingmyocardial
infarction;preventingdamageadministratedimmediatelyafterattackAsparaginase:regressionSeveralr