Enzyme Classification

Questions and Answers

Ester, ether, peptide or glycosidic bonds (correct)

Peptide or glycosidic bonds only

Ether or glycosidic bonds only

Ester or peptide bonds only

Choline esterase

Acetyl choline esterase

Acetyl choline hydrolase (correct)

Choline acetate hydrolase

Isomerase

Hydrolase

Lyase (correct)

Ligase

Optical, geometric or positional Signup and view all the answers

Linking of substrates Signup and view all the answers

Synthetase requires ATP, synthase does not Signup and view all the answers

To provide an unambiguous way of naming enzymes Signup and view all the answers

-ase Signup and view all the answers

To catalyse the oxidation of one substrate with simultaneous reduction of another substrate or co-enzyme Signup and view all the answers

EC.1.1.1.1 Signup and view all the answers

ATP-Hexose-6-phosphatetransferase Signup and view all the answers

6 Signup and view all the answers

To transfer one group from the substrate to another substrate Signup and view all the answers

The class of the enzyme Signup and view all the answers

Study Notes

Early enzymes were given whimsical names, such as Pepsin, Trypsin, and Chymotrypsin, which are still used today.
Later, enzymes were named by adding the suffix "-ase" to the substrate, for example, Lactase acts on lactose to form glucose and galactose.

The International Union of Biochemistry and Molecular Biology (IUBMB) developed a system of nomenclature for enzymes in 1964, modified in 1972 and 1978.
The system uses a four-digit code starting with EC (enzyme class), followed by:
- First digit: class
- Second digit: subclass
- Third digit: sub-subclass or subgroup
- Fourth digit: number of the particular enzyme in the list

Class 1: Oxidoreductases
- Catalyze oxidation of one substrate with simultaneous reduction of another substrate or co-enzyme
- Example: Alcohol dehydrogenase (Alcohol-NAD-oxidoreductase; EC.1.1.1.1)
Class 2: Transferases
- Transfer one group (other than hydrogen) from the substrate to another substrate
- Example: Hexokinase (ATP-Hexose-6-phosphatetransferase)
Class 3: Hydrolases
- Hydrolyze ester, ether, peptide, or glycosidic bonds by adding water
- Example: Acetyl choline esterase or Acetyl choline hydrolase
Class 4: Lyases
- Remove groups from substrates or break bonds by mechanisms other than hydrolysis
- Example: Aldolase
Class 5: Isomerases
- Produce optical, geometric, or positional isomers of substrates
- Example: Triose phosphate isomerase
Class 6: Ligases
- Link two substrates together, usually with simultaneous hydrolysis of ATP
- Example: Acetyl CoA carboxylase