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8/7/2019 ENZYME-1 irfan raza

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ENZYMES


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Biological catalysts which speed up the

rate of reaction without becoming part of

the reaction

Enzymes increases the rate of reaction by

lowering the activation energy barrier,

thus allowing reactions to proceedwithout an input of energy

What are Enzymes


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Enzyme Nomenclature

Recommended Name:Suffix ase attached to the susbtrate of the

reaction

For example; Glucosidase, Urease

Systematic Name

IUBMB divided enzymes into six classes

The suffix ase is attached to describe

complete chemical reaction and substratename

For example; Pyruvate decarboylase


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How Enzyme Works

Active site - a region of an enzymecomprised of different amino acids where

catalysis occurs

Substrate - the molecule being utilized

and/or modified by a particular enzyme at

its active site

Co-factor - organic or inorganic

molecules that are required by enzymesfor activity.


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Enzymes convert substrates into products

What is a substrate?

A substrate is the compound that is converted intothe product in an enzyme catalyzed reaction.

For the reaction catalyzed by aldolase, fructose 1,6-phosphate is the substrate.

Fructose 1,6-phosphate

Glyceraldehyde3-phosphate

Dihydroxyacetonephosphate

+

aldolase

Substrate Products


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Enzyme Physical Nature

Apoenzyme = the protein part of an enzyme

without coenzymes or prosthetic groups that

are required for the enzyme to have activity.

Coenzyme = small organic molecules which is

dialyzable, thermostable and loosely attachedto the protein part.

Prosthetic group = an organic substance

which is dialyzable and thermostable which is

firmly attached to the protein or apoenzymeportion.

Cofactors= Inorganic molecules


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Cofactors

Non-protein molecules that help

enzymes function.

Bind to active site to enhanceenzymatic reactions.

Cofactors may be inorganic metals

such as zinc, iron, or copper.


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COENZYMES

Heat stable, low mol wt organiccompounds, non-covalently linked withenzymes, can be separated.

APO + CO = Holoenzyme

Act as intermediate or ultimate acceptor

in group transfer


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Important Coenzymes

NAD+

NADP+

FAD Coenzyme A


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CO-ENZYMES

REDUCTION OF NAD+ TO NADH.H+

Lactic acid + NAD Pyruvic acid + NADH-H+

Glucose-6-phos+ NADP 6-Phosphoglucon-olactone +NADPH-H+

RED

UCTION OF FAD

OR FMN TO FADH

2 OR FMNH2

FMN is co enzyme for cytochrome C oxidase,L.Amino acid dehydrogenase

FAD is co-enzyme for xanthene oxidase acyl-CoAdehydrogenase

LDH

G-6-P.D


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CO-ENZYMES

Thiamine pyrophosphate:

Co-enzyme for oxidative decarboxylation for

ketoacids

Pyruvate Acetyl CoA

Pyruvate+TPP Acetalaldehyde-TPPcomplex+Co2

Pyruvate decarboxylase

Pyruvate dehydrogenase

CoA NAD NADH-H+


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CO-ENZYMESBiotin

Part of multiunit enzymes causing carboxylation reactions.Acts as carrier of CO2

Acetyl CoA+HCo3 + ATP Malonyl-CoA

NH4+HCo3 + 2ATP Carbmoyl PO4 +2ADP+ 2 Pi

Acetylcarboxylase

Enz-Biotin-COO-p Enz-Biotin

Carbamoyl Po4.Synthetase - Biotin


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CO-ENZYMESAscorbic acid (Vitamin C)

Required for hydroxylation of proline into hydroxyproline forsynthesis of collagen

Bile acid formation

Conversion of cholesterol into 7-hydroxylcholesterol

Maintain metalic co-factors like Cu+ in Monooxygenases and Fe

in dioxygenases in reduced form Conversion of cholesterol into steroid hormone in adrenal

cortex

Absorption of iron by reducing into reduced form which is canbe easily absorbed

Acts as antioxidant in GIT by preventing formation ofnitrosamines during digestion


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CO-ENZYMES

Folic acid Active form is tetrahydrofolate which acts as single

carbon carrier for synthesis of various compounds

like pyrimidines and purines

Vitamin B12 Acts as co-enzyme in groups rearrangements in

isomerases e.g. conversion of methyl malonyl CoA

into succinyl-CoA

by enzyme methylmalonyl-CoA

mutase

Converts homocysteins into methionine

Act as maturation factor for RBCs


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Oxidoreductases catalyze the transferof hydrogen atoms and electrons

Example - Lactate Dehydrogenase

O O -

C

C

C H 3

O + NAD H + H +

O O -

C H

C

C H3

H O + NAD +

pyruvate L-lactate

lactatedehydrogenase

CLASSIFICATION


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Hydrolases catalyze the cleavage of bonds by

the addition ofwater (hydrolysis)

Example - Trypsin

NH

C

NH 2(C H 2) 4H

O

C

O

HH

CNH

NH

C

C H 3H

O

C

O

H

CNH

CC

C H (C H3)2

NH

C

NH 2(C H 2) 4H

O

C

O

HH

C

NH

O-C

NH

C

C H3 H

O

C

O

C H (C H3)2H

CH 3 N+ C

+ H2Otrypsin

+

G ly -Lys - V a l - A l a

V a l - A l a

G ly -Lys


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Lyases catalyze the cleavage ofC-C,C-O,

or C-N bonds

(addition of groups todouble bonds or formationofdouble bonds by removal of groups)

Example - ATP-citrate lyase

O O -

C

C

C H 2

O

O O-

C

oxaloacetate

O O -

C H 2

C

C H 2

O O -C

CO

O -

CH O

citrate

O C H 3C

O -

acetate

TP-citratelyase

+

TP P + P i

Coenzy e


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Isomerases catalyze the transfer of functional

groups within the same molecule

Example - Phosphoglucose isomerase

O H

H C

C

C HH O

H C

O O P O 32-

C

O H

H C O HO H

glucose 6-phosphate

C

C H 2 O H

C HH O

H C

C

O

H C O H

O H

O P O 32-

O

fructose 6-phosphate

phosphoglucoseiso erase


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Ligases use ATP to catalyze the

formation of new covalent bonds

Example - DNA ligase

O-O

O

O-

HO

3'

5' 3'

5'

T G C A G

T CG

O

O -

O

O -

OH

3'

3'

5'

GCT CA

CGA

5'

+O

O

O O

O

O -

O O -

G CT

GACGT

5'

3'5'

3'

A G C

A CT C G

5'

3'

3'

5'

DNA ligase

AT AD + i


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Summary: Enzyme classes and major subclasses

Oxidoreductases

Dehydrogenases

Oxidases

Reductases

Peroxidases

Catalase

Oxygenases

H

yd

rox

ylases

HydrolasesEsterases

Glycosidases

Peptidases

Phosphatases

Thiolases

Phospholipases

Amidases

Deaminases

Ribonucleases

TransferasesTransaldolase

Transketolase

Acyltransferase

Methyltransferase

Glucosyltransferase

Phosphoryltransferase

Kinases

Phosphomutases


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Summary: Enzyme classes and major subclasses

Lyases

Decarboxylases

Aldolases

Hydratases

Dehydratases

Synthases

Lyases

Ligases

Synthetases

Carboxylases

Isomerases

Racemases

Epimerases

Isomerases

Some mutases


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Enzyme Catalysis Overview


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Factors Influencing Enzyme

Activity

Enzyme concentration

Temperature

pH

Substrate concentration

Inhibitors


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Enzyme Concentration

substrate must be present in an excess amount; i.e., the

reaction must be independent of the substrateconcentration. Any change in the amount of product

formed over a specified period of time will be dependent

upon the level of enzyme present.


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Substrate ConcentrationIf the amount of the enzyme is kept constant and the

substrate concentration is then gradually increased, the

reaction velocity will increase until it reaches a maximum.


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A reaction rate will generally

increase with increasingTemperature due to increased

kinetic energy in the system

until a maximal velocity is

reached. Above this maximum,

the kinetic energy of the

system exceeds the energy

barrier for breaking weak

H-bonds and hydrophobic

interactions, thus leading tounfolding and denaturation of

the enzyme and a decrease in

reaction rate.

Effect of Temperature


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Variations in pH can affect a

particular enzyme in many

ways, especially if ionizable

amino acid side chains areinvolved in binding of the

substrate and/or catalysis.

Extremes of pH can also lead to

denaturation of an enzyme ifthe ionization state of amino

acid(s) critical to correct folding

are altered. The effects of pH

and temperature will vary for

different enzymes

Effect of pH


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What is an isozyme?

(1) Isozymes are physically distinct forms ofthe same enzyme.

(2) Isozymes may differ from each other by

differences in their amino acid sequences or

by the presence of different posttranslational

modifications in each isozyme.

(3) The relative abundance of different

isozymes varies for different tissues.


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MICHEALIS MENTON EQUATION

V1=V max [5]

mk + {S}

V1= Measured initial velocity

V max = Maximum velocity

S = Substrate

Km = Michaelis constant

VariationsWhen (S) is much less than Km

V1= V max [5] OR V max [S] K [S]

mk + {S} Km


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Figure 5.7ab

Enzyme Inhibitors: Competitive

Inhibition


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Enzyme Inhibitors:

Noncompetitive Inhibition


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Medical Relevance

Many diseases are caused by the absence, malfunction,or inappropriate expression

of a particular enzyme---SOD

Enzymes serve as targets for a variety ofdrugs

Enzymes are sometimes administered in

the treatment ofdisease The presence or absence of specific

enzymes can be used todiagnose specific

diseases


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Clinical Use of Enzymes

EnzymeActivity in Body Fluids Reflects OrganStatus:

Cells die and release intracellular contents;

increased serum activity of an enzyme can be

correlated with quantity or severity of damagedtissues (ex. creatine kinase levels following heart

attack)

Increased enzyme synthesis can be induced and

release in serum correlates with degree of

stimulation (ex. alkaline phosphatase activity as a

liver status marker)


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Serum enzymes are commonly used in

diagnostic tests for a variety ofdiseases

Myocardial Infarction: Lactate dehydrogenase (H4

isozyme), Aspartate aminotransferase,Creatine

kinase

Viral hepatitis: Alanine aminotransferase

Acute pancreatitis: Amylase,Lipase

Liver disease: Alkaline phosphatase,Lactate

dehydrogenase (M4 isozyme)

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