Introduction, Properties, Nomenclature and IUBMB Classification of Enzymes

Introduction and Properties

The International Union of Biochemistry and Molecular Biology (IUBMB) is an organization that deals with biochemistry and molecular biology. At present, the IUBMB consists of 79 members. A major objective of the Union is to promote biochemistry and molecular biology research and education throughout the world, with special attention given to areas that are in their early stages of development.

The first Congress of Biochemistry was organized by Sir Hans Adolf Krebs in Cambridge, UK, in 1949 in order to encourage collaboration between biochemists separated by World War II. Biochemistry was a growing discipline at that time and was seeking to establish its Union within the International Council for Science. Biochemistry was recognized for the first time as a distinct discipline at Congress. A final session was held at which the International Committee of Biochemistry was established with twenty members from 14 countries, aiming to obtain recognition from the International Council of Science as the global representative of biochemistry soon. In 1955, the Third Congress of Biochemistry in Brussels formally admitted the International Union of Biochemistry (IUB) to the ICSU after several years of debate. The International Union of Biochemistry and Molecular Biology (IUBMB) was renamed IUBMB in 1991.

Classification of Enzymes and Nomenclature

Chemical reactions are catalyzed by biological polymers. Neither enzymes are consumed nor permanently altered as a result of their participation in reactions. All enzymes in nature are proteins except ribozymes, which catalyze RNA molecules. Besides having high efficiency, enzymes is also highly selective catalysts.

Enzyme nomenclature depends on a number of factors, including,

• A variety of substrates may be used
• Trivial names
• It is also based on its regulations
• Source of enzymes
• Enter the name of the reaction (and the suffix -ase) that is catalyzed

Type on the reaction that is catalyzed (and then by suffix-ase)

• Protease
• Transferase
• Reductase
• Dehydrogenase
• Isomerase

Nature of substrate

• Hexokinase
• Alcohol dehydrogenase
• Glucokinase
• Xanthine oxidase

Source of enzyme

• Gastric lipase
• Salivary amylase
• Pancreatic lipase
• Muscle phosphorylase
• Hepatic phosphorylase

Based on its regulation

• Pepsin
• Hormone specific lipase
• Thrombin
• Trypsin

Systematic Names of Enzymes

Classification based IUB – international union of biochemistry

By using specific code numbers and unique names, each enzyme is identified by the type of reaction it catalyzes and the type of substrate it uses.

There are six groups classified for enzymes

Class 1 – oxidoreductase

A reduction equivalent(hydrogen or electrons) is transferred from one redox system to another by oxidoreductases.
Example – lactate dehydrogenase, xanthine oxidase, cytochrome oxidase, alcohol dehydrogenase, aldehyde dehydrogenase, oxidase,

Class 2 – Transferases

Catalyzing the transfer of other groups between molecules, the transferases function. Coenzymes are generally needed by oxidoreductases and transferases.
Example – methyltransferase, phosphotransferase, aminotransferase,

Class 3 - hydrolases

Water is used to cleave bonds by the hydrolases.
Example – peptidase, glycosidase, protease, phosphatase

Class 4 - lyases

The Lyases catalyze reactions in which chemical bonds are either formed or cleaved (also known as synthases), with double bonds either establishing or fading away. Water is not required for the cleavage of bonds. The C-C, C-O, C-N, and C-S bonds are normally broken by lyases.
Example – glutamate decarboxylase, fumarase, argininsuccinase

Class 5 – isomerase

As the isomerases move groups inside molecules, they do not change the constituents of the substrate.
Example – aldose ketose isomerase, mutase, epimerase

Class 6 - ligases

Ligases (synthetases, class 6) catalyze ligation reactions with energy, which are always accompanied by nucleoside triphosphate hydrolysis.
Example – pyruvate carboxylase, DNA ligase, acetyl Co-A carboxylase

EC number (enzyme commission number)

The enzymes in the Enzyme Catalogue are assigned EC numbers (Enzyme Commission numbers). Each enzyme belongs to one of six main classes. There are also subclasses and subclasses below. IUB names two enzymes that belong to the same sub-subclass. Hexokinase is ATP: D-hexose 6-phosphotransferase E.C.2.7.1.1. Hexokinase belongs to subclass 7 of class 2 (transferases), which regulates phosphorylation with subclass 1 (here alcohol is considered as phosphoryl receptor) plus there is hexose –6 that refers that the alcohol is phosphorylated on the sixth carbon of the hexose. The enzyme is still known as hexokinase.

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