Enzyme Classification Lect 2

8/8/2019 Enzyme Classification Lect 2

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ENZYME CLASSIFICATIONLECTURE -2

PUNIMA PURI


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Enzyme nomenclature is recommended by Enzyme

Commission which was set up in 1955 by International

Union of Biochemistry and Molecular Biology (IUBMB)

It classified the enzyme on the basis of kind of reaction

they performed, substrate they act, position of group or

functional groups and number of amino acid.

The full systemic name of enzyme shows not only the

type of reaction catalyzed but also describes the substrate

acted on and product produced and other information.


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CLASSIFICATION OF ENZYME

OXIDOREDUCTASES

TRANSFERASES

HYDROLASES

LYASES

ISOMERASES

LIGASES

Punima Puri


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EC number system

1 number class of enzyme(1-6)

2 number subclass by the type of substrate or bond

cleaved

3 number sub-subclass allowing more precise definition

of reaction catalyzed in the term of electron acceptor or

groups removed

4 number serial number of enzyme in its sub-subclass

Classification based on chemical reaction catalyzed not

by the source (species, tissues of enzyme.)


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Enzyme classification

1.Oxidoreductases - catalyzing oxidation reduction

reactions.

2.Transferases - catalyzing transfer of functional

groups.3.Hydrolases - catalyzing hydrolysis reactions.

4.Lyases - catalyzing group elimination reactions to

form double bonds.

5.Isomerases - catalyzing isomerizations (bondrearrangements).

6.Ligases - catalyzing bond formation reactions couples

with ATP hydrolysis.


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Oxidoreductases

y Oxidoreductases - enzymes that transfer electron from

molecule to another during oxidation reaction:

y A + B- -> A- + B

Usually this oxidation process involves removing of

the hydrogenatom.

y In some rare cases the oxidation reaction involves theoxygen molecules (O2), then enzymes are

named oxidase

Punima Puri


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Lactate dehyrogenase

CH3CH(OH)COO-+NAD+ CH3COO

-+NADH++H+

Eg S lactate NAD + oxidoreductases (EC 1.1.1.27)

S lactate is the substrate and NAD+ electron

acceptor/hydrogen acceptor and type of reaction

catalysed is of oxidation.

EC number 1 digit denotes type of the reaction i.e

oxidoreductase

2 digit functional group of lactate which is alcohol

therefore denoted by subclass 1

3 digit denotes NAD as electron acceptor

4 digit is actual substrate.


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OXIDOREDUCTASES

1.1Acting on the CH-OH group of donors

1.1.1. With NAD or NADP as acceptor

1.1.2. With a cytochrome as acceptor

1.1.3.With oxygen as acceptor

1.1.4.With a disulfide as acceptor

1.1.5.With a quinone or similar compound as acceptor

1.1.99. With other acceptors

1.2Acting on the aldehyde or oxo group of donors

1.3Acting on the CH-CH group of donors

1.4Acting on the CH-NH2

group of donors


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y This classification is based on substrate utilised

by enzymes.

y EC1.1 - Substrate contains the CH-OH group.These dehydrogenases acts on alcohols and

hemi-acetals.

y EC1.2 - Substrate contains the aldehyde or

oxo group. These dehydrogenases acts on

aldehydes.

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y EC1.3 - Substrate contains the CH-CH group. These

dehydrogenases introduce double bond by direct

dehydrogenation of a single bond.

y EC1.4 - Substrate contains the CH-NH2 group. Amino

acid dehydrogenases.

y EC1.5 - Substrate contains the CH-NH group. Theseenzymes converts secondary amines by introducing of

double bond C=N.

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y EC1.6 - Substrates are NADH or NADPH. The

catalytically important is reverse reaction -

reduction of the substrate with NAD

+

orNADP+ acceptors.

y EC1.7 - Donor for other nitrogenous compounds.

y EC1.8 - Substrate contains a sulphur group.

Substrates usually inorganic or organic thiols.

y EC1.9 - Substrate contains a heme group.Cytochrome oxidases and nitrate reductases are

member of this group.

Punima Puri


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TRANSFERASES

Transfer functional groups between donor and

acceptor molecules.

Kinases are specialized transferases that regulate

metabolism by transferring phosphate from ATP to

other molecules.

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y A very basic reaction catalysed by transferase can bedescribed in the following diagram:

y A-X + B -> A + B-X

when the catalyst is added and the reaction proceeds,the X is removed from the A faster than it normallywould be without an enzyme and then transferred to

the B.

y This reaction is used to make a name for all this classof enzymes.

y Transfer - is a first part of the word transferase, andthe second part of the word -ase is common part forall enzymes.

Punima Puri


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TRANSFERASES

2.1 Transferring one-carbon groups

2.1.1. Methyltransferases

2.1.2. Hydroxymethyl-, Formyl- and Related

Transferases2.1.3. Carboxyl- and Carbamoyltransferases

2.1.4. Amidinotransferases

2.2 Transferring aldehyde or ketonic groups

2.3 Acyltransferases

2.4 Glycosyltransferase


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HYDROLASES

3.1 Acting on ester bonds

3.1.1 Carboxylic Ester Hydrolases

3.1.2 Thiolester Hydrolases

3.1.3 Phosphoric Monoester Hydrolases 3.1.4 Phosphoric Diester Hydrolases

3.1.5 Triphosphoric Monoester Hydrolases

3.2 Glycosylases

3.3 Acting on ether bonds 3.4 Acting on peptide bonds (peptidases)

Eg sucrase, amylase, lipase


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LYASES

4.1Carbon-carbon lyases

4.1.1 Carboxy-lyases

4.1.2 Aldehyde-lyases

4.1.3 Oxo-acid-lyases 4.1.99 Other Carbon-carbon lyases

4.2 Carbon-oxygen lyases

4.3 Carbon-nitrogen lyases

4.4 Carbon-sulfur lyases 4.5 Carbon-halide lyases

Eg decarboxylase


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ISOMERASES

5.1 Racemases and epimerases

5.1.1. Acting on Amino Acids and Derivatives

5.1.2. Acting on Hydroxy Acids and Derivatives

5.1.3. Acting on Carbohydrates and Derivatives

5.1.99. Acting on Other Compounds

5.2cis-trans-Isomerases

5.3Intramolecular isomerases

5.4Intramolecular transferases (mutases)

5.5Intramolecular lyases 5.99Other isomerases

Eg alanine racemase catalyses conversion of L lysine toD lysine.


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LIGASES

6.1 Forming carbonoxygen bonds

6.1.1. Ligases Forming Aminoacyl-tRNA and

Related Compounds

6.2Forming carbonsulfur bonds

6.2.1. Ligases Forming Aminoacyl-tRNA andRelated Compounds

6.3Forming carbonnitrogen bonds

6.4Forming carboncarbon bonds

6.5Forming phosphoric ester bonds

Eg isoleucine tRNA ligase (bonding of isoleucine withspecific tRNA acceptor)

ATP+L-isoleucine+tRNAile = AMP + pyrophosphate +L-isoleucyl-tRNAile

Documents

Enzyme Classification Lect 2