naming and classification of enzyme
Published on: Mar 3, 2016
Transcripts - Namingandclassification
JESSA S. ARIÑO BSE-3BCentral Bicol State University of Agriculture
Enzymes are most commonly named by using a system that attempts to provide information about the function rather than the structure of the enzyme. Type of reaction catalyzed and substrate identity are focal points for the nomenclature. A substrate is the reactant in an enzyme- catalyzed reaction.
1. The suffix –ase identifies a substance as an enzyme. The suffix –in is still found in the name of the first enzymes studied such as trypsin, chymotrypsin, and pepsin.2. The type of reaction catalyzed by an enzyme is often noted with a prefix. oxidase- catalyzes oxidation reaction hydrolase- catalyzes a hydrolysis reaction
3. The identity of the substrate is often noted in addition to the type of reaction.glucose oxidase- catalyzes oxidation of glucoselactate dehydrogenase- catalyzes the removal of hydrogen from lactate ion.Infrequently, the substrate but not the reaction type is given:Urease- catalyses the hydrolysis of ureaLactase- catalyses the hydrolysis of lactose
According to the International union Of Biochemistry an enzyme name has two parts: -First part is the name of the substrates for the enzyme. -Second part is the type of reaction catalyzed by the enzyme. This part ends with the suffix “ase”.Example: Lactate dehydrogenase
The International Union of Biochemistry and Molecular Biology have developed a nomenclature for enzymes, the EC numbers; each enzyme is described by a sequence of four numbers preceded by "EC". The first number classifies the enzyme based on its mechanism.
Enzymes are classified into six different groups according to the reaction being catalyzed. The nomenclature was determined by the Enzyme Commission in 1961 (with the latest update having occurred in 1992), hence all enzymes are assigned an “EC” number. The classification does not take into account amino acid sequence (ie, homology), protein structure, or chemical mechanism.
EC numbers are four digits, for example a.b.c.d, where “a” is the class, “b” is the subclass, “c” is the sub-subclass, and “d” is the sub-sub-subclass. The “b” and “c” digits describe the reaction, while the “d” digit is used to distinguish between different enzymes of the same function based on the actual substrate in the reaction. Example: for Alcohol:NAD+oxidoreductase EC number is 22.214.171.124
EC 1. Oxidoreductases EC 2. Transferases EC 3. Hydrolases EC 4. Lyases EC 5. Isomerases EC 6. Ligases A list of the subclasses for each class is given below. Additional information on the sub-subclasses and sub- sub-subclasses (ie, full enzyme classification and names) can be found at the referenced web link. From the Web version, http://www.chem.qmul.ac.uk/iubmb/enzyme/index.ht ml
EC 1. Oxidoreductases :catalyze the transfer of hydrogen or oxygen atoms or electrons from one substrate to another, also called oxidases, dehydrogenases, or reductases. Note that since these are ‘redox’ reactions, an electron donor/acceptor is also required to complete the reaction.
EC 2. Transferases – catalyze group transfer reactions, excluding oxidoreductases (which transfer hydrogen or oxygen and are EC 1). These are of the general form: A-X + B ↔ BX + A
EC 3. Hydrolases – catalyze hydrolytic reactions. Includes lipases, esterases, nitrilases, peptidases/proteases. These are of the general form: A-X + H2O ↔ X-OH + HA
MaltaseMaltose Glucose Glucose
EC 4. Lyases – catalyze non-hydrolytic (covered in EC 3) removal of functional groups from substrates, often creating a double bond in the product; or the reverse reaction, ie, addition of function groups across a double bond. A-B → A=B + X-Y X Y Includes decarboxylases and aldolases in the removal direction, and synthases in the addition direction.
EC 5. Isomerases – catalyzes isomerization reactions, including racemizations and cis- tran isomerizations.
EC 6. Ligases -- catalyzes the synthesis of various (mostly C-X) bonds, coupled with the breakdown of energy-containing substrates, usually ATP
a. Cellulaseb. L- amino acid oxidasec. Sucrased. Maltasee. Succinate dehydrogenase
Group Reaction catalyzed Typical reaction Enzyme example(s) with trivial nameEC 1 To catalyze oxidation/reduction AH + B → A + BH Dehydrogenase, oxidaseOxidoreductases reactions; transfer of H and O atoms (reduced) or electrons from one substance to A + O → AO another (oxidized)EC 2 Transfer of a functional group from one AB + C → A + BC Transaminase, kinaseTransferases substance to another. The group may be methyl-, acyl-, amino- or phosphate groupEC 3 Formation of two products from a AB + H2O → AOH Lipase, amylase, peptidaseHydrolases substrate by hydrolysis + BHEC 4 Non-hydrolytic addition or removal of RCOCOOH → DecarboxylaseLyases groups from substrates. C-C, C-N, C-O RCOH + CO2 or or C-S bonds may be cleaved [X-A-B-Y] → [A=B + X-Y]EC 5 Intramolecule rearrangement, AB → BA Isomerase, mutaseIsomerases i.e. isomerization changes within a single moleculeEC 6 Join together two molecules by X + Y+ ATP → XY SynthetaseLigases synthesis of new C-O, C-S, C-N or C- + ADP + Pi C bonds with simultaneous breakdown of ATP
A. CELLULASE catalyzes the hydrolysis of celluloseB. L-AMINO ACID OXIDASE catalyses the oxidation of L-amino acids.C. SUCRASE catalyses the hydrolysis of the disaccharide sucroseD. MALTASE catalyses the hydrolysis of the disaccharide maltoseE. SUCCINATE DEHYDROGENASE catalyzes the removal of hydrogen from succinate ion