1. 20.2 Classification of Enzymes
Enzyme names describe the compound or the reaction that is catalyzed. The ribbon structure for alanine transaminase, an aminotransferase, contains 495 amino acid residues.
Learning Goal Classify enzymes and give their names.

2. Names of Enzymes The name of an enzyme usually ends in ase.
identifies the reacting substance; for example, sucrase catalyzes the reaction of sucrose.
describes the function of the enzyme; for example, oxidases catalyze oxidation.
can be a common name, particularly for the digestive enzymes, such as pepsin and trypsin.

3. Enzyme Class, Oxidoreductases
The Enzyme Commission of the International Union of Biochemistry and Molecular Biology systematically classifies enzymes according to the six general types of reactions they catalyze (Table 20.2). Core Chemistry Skill Classifying Enzymes

4. Enzyme Classes, Transferases, Hydrolases

5. Enzyme Classes, Lyases, Isomerases

6. Enzyme Classes, Ligases

7. Study Check
Match the type of reaction with an enzyme. 1) aminase 2) dehydrogenase 3) isomerase 4) synthetase A. converts a cis fatty acid to a trans fatty acid B. removes two H atoms to form a double bond C. combines two molecules to make a new compound D. adds NH3

8. Solution
Match the type of reaction with an enzyme. 1) aminase 2) dehydrogenase 3) isomerase 4) synthetase 3 A. converts a cis fatty acid to a trans fatty acid 2 B. removes two H atoms to form a double bond 4 C. combines two molecules to make a new compound 1 D. adds NH3

9. Chemistry Link to Health: Isoenzymes As Diagnostic Tools
are different forms of an enzyme that catalyze the same reaction in different cells or tissues of the body.
have quaternary structures with slight variations in the amino acids in the polypeptide subunits.
There are five isoenzymes of lactate dehydrogenase (LDH) that catalyze the conversion between lactate and pyruvate.

10. Chemistry Link to Health: Isoenzymes As Diagnostic Tools
Myocardial infarction may be indicated by an increase in the levels of creatine kinase (CK) and lactate dehydrogenase (LDH).
The different forms of an enzyme allow a medical diagnosis of damage or disease to a particular organ or tissue.

11. Chemistry Link to Health: Isoenzymes As Diagnostic Tools
The different isoenzymes of lactate dehydrogenase (LDH) indicate damage to different organs in the body.