EnzymE nomenclature in enzymology....ppt

This is a guide on the classification and nomenclature of enzymes

1. A. J. Alhassan Enzymes Classification and
Nomenclature
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Classification and
nomenclature of enzymes

2. A. J. Alhassan Enzymes Classification and
Nomenclature
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 ‘trivial’ names are names used to denote enzymes in the
olden days.
 ‘trivial’ names consisted of the suffix –‘ase’ added to the
substrate acted upon or type of reaction catalyzed, by the
enzymes.
 some trivial names explain nothing about the substrate or
reaction catalyzed.
 Hence in 1955 the international Union of Biochemistry
in consultation with international union of Pure and
applied chemistry set up enzyme commission.
 The commission came up with systematic nomenclature
of the ever increasing number of enzymes by
categorizing enzyme catalyzed reaction into six classes

3. A. J. Alhassan Enzymes Classification and
Nomenclature
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Class of reaction Reaction Catalyzed Enzymes

1 Oxidation – reduction reactions catalyzed by oxidoreductases.

2 group transfer reactions “ “ transferases.
3 hydrolytic reactions “ “ hydrolases

4 “ “ lyases.

5 isomerization reactions “ “ isomerases
6 “ “ ligases
Elimination reaction in which
a double bond is form
reaction in which 2 molecules are
joined at the expense of an energy
(usually in form of ATP)

4. A. J. Alhassan Enzymes Classification and
Nomenclature
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 A complete systematic name of enzyme shows;
 type of reaction catalyzed,
 the substrates acted on
 other important information.
 an enzyme from each major class is given below
 Class 1: eg. lactate dehydrogenase
The full systematic name is lactate: NAD+ oxidoreductase which shows that L-lactate
acts as the electron donor and NAD+ is the e- acceptor.
L –lactate + NAD+ pyruvate + NADH + H+
Class 2: e.g. hexokinase
The full systematic name is ATP: D-hexose 6-phosphotransferase, indicating that ATP
is the phosphate donor, a D-hexose the phosphate acceptor and that transfer is to the
hydroxyl group on C6 of the hexose.
ATP + D-hexose ADP + D- hexose 6 - phosphate

5. A. J. Alhassan Enzymes Classification and
Nomenclature
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Class 3: eg adenosinetriphosphatase.
The full name is ATP phosphohydrolase, indicating that ATP (the substrate) is
hydrolyzed so as to split the bond which allows release of orthophosphate:
ATP + H
2
O ADP + P
i
Class 4: eg fructose bisphosphate aldolase.
Full name is D- fructose I, 6-bisphosphate D – glycerdehyde 3- phosphate –
lyase,
which indicates that the substrates D-fructose 1,6 –bisphosphate is cleaved
in
such a way as to yield D-glyceraldehydes 3- phosphate as one of the
products.D-fructose 1, 6-diphosphate glyceraldytes 3-phos + DHAP

6. A. J. Alhassan Enzymes Classification and
Nomenclature
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Class 5: eg triose phosphate isomerase
Full systematic name is D-glyceraldehyde 3-phosphate ketol- isomerase,
indicating that aldose D-glyceraldehyde 3-phosphate is isomerized to the
ketose
dihydroxyacetone phosphate
D-glyceraldehyde 3-phosphate DHAP
Class 6: eg. isoleucyl- tRNA synthetase
Full systematic name is L-isoleucine: tRNA
ile
ligase (AMP-truming) and it
indicates
that L-isoleucine becomes bonded to a specific tRAN acceptor (tRNA
ile
) and
that in
the process ATP is split to AMP and PP
i
ATP+ L-isoleucine+ tRNA
ile
AMP+ PP
i
+ L-isoleucyl-tRNA
ile
.
 However trivial are now adopted for daily used as recommended names for the fact
that systematic name of enzymes are cumbersome
 Enzymes are further classified by being assigned an EC number which consist of 4
parts (a,b,c,d).

7. A. J. Alhassan Enzymes Classification and
Nomenclature
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 The first number (a) indicates the type of reaction catalyzed and can take value from
1-6 according to the classification of types given above.
 The 2nd number (b) indicates the subclass which usually specified the type of
substrates or bond cleaved more precisely. For eg in the case of oxidoreductases,
It shows the type of chemical grouping acting as an electron donor whereas in
hydrolases it shows the type of bond being broken.
 The 3rd number (c) indicates the sub-subclass which allow for more precise definition
of the reaction catalyzed. For eg in oxidoreductases it specified the type of electron
acceptor and in lyases the type of group removed.
 The 4th number (d) indicates the serial № of the enzyme in the sub-subclass.
 System of nomenclature and classification can not distinguished between
Adenosinetriphosphatases from IMM and ,SPR they concern with transport of
protons and Ca2+ respectively, however what have in common is the power to
hydrolyzed ATP.

 for more exact specification of enzymes source and isoenzyme type should be
mentioned

8. A. J. Alhassan Enzymes Classification and
Nomenclature
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Multienzyme systems:
 EC recommendation is that where more than a catalytic activity is to be ascribed it
should be referred to as system eg fatty acid synthase system.
Isoenzymes:
 They are enzymes catalyzing the same reaction but differ in;
• amino acid sequence
• covalent modification (e.g. phsophorylation of serine OH groups)
• in their 3DS (conformation)
 The term isoenzymes refers to those forms of enzymes that arise from
genetically determined differences in amino acid sequence but not to those
derived by modification of the same amino acid sequence.

9. A. J. Alhassan Enzymes Classification and
Nomenclature
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Their electrophoretic mobility gives the basis for their nomenclature
It is recommended that naming of isoenzymes should be based on
extend of migration in an applied electric field.
The isoenzymes are numbered starting with the species having the highest
mobility to wards the anode.
 two different LDH subunits exist in an organism M and H
These subunits can associate to form tetramers randomly, a total of five
different isoenzymes of LDH are found in the body.
 sections from the amino acid sequences of the two subunits using the
single- letter notation is given in fig. below.

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Nomenclature
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A common precursor gene was probably duplicated at some point in
evolution.
 The two genes then continued to develop further independently of each
other through mutation and selection.