If the first number in an Enzyme Commission number is 1, which class of enzyme does it represent?

The first number in an Enzyme Commission (EC) number indicates the class of the enzyme according to the system established by the International Union of Biochemistry and Molecular Biology (IUBMB). When the first digit is '1', it designates the enzyme as an oxidoreductase.

Oxidoreductases are enzymes that catalyze oxidation-reduction reactions, where one substrate is oxidized and another is reduced. This class of enzymes plays vital roles in many metabolic pathways, such as cellular respiration and photosynthesis. They are essential for processes that involve the transfer of electrons, making them key players in energy production and biosynthesis within the cell.

In contrast, other classes of enzymes have different first digits: '2' corresponds to transferases, which transfer functional groups between different molecules; '3' denotes hydrolases, which catalyze hydrolysis reactions; and '4' refers to lyases, which are involved in the addition or removal of groups to form double bonds. Each of these classes serves a distinct purpose in biological processes, and understanding these classifications is fundamental for anyone studying biochemistry or enzymology.