Biochemistry - The Chemical Reactions of Living Cells, Volume 2 - D. Metzler 1980

Types of reactions catalyzed by enzymes
Addition and elimination reactions
Addition to polarized double bonds (Type 2.A reaction, Table 7-1)

Along with direct Nucleophilic substitution reactions, addition reactions to double bonds and their reverse elimination reactions are among the most common processes in Enzymatic Catalysis.

Alcohols, thiols, and amines readily add to the electrophilic carbon atom of a carbonyl group, forming hemiacetals, hemiketals, hemimerkaptals, and carbinolamines. A well-known example is The formation of cyclic sugar structures [Equation (6-75)]. Water can also add to carbonyl groups. For instance, in aqueous solution, acetaldehyde exists as an equilibrium mixture consisting of 50% free aldehyde and 50% hydrate [99]:

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whereas formaldehyde is more than 99.9% hydrated [100].

Addition reactions frequently serve as one of the steps in more complex enzyme-catalyzed pathways. For example, the thiol group of glyceraldehyde-3-phosphate dehydrogenase reacts with the aldehyde substrate to form a hemimerkaptal, which is subsequently oxidized to a thioester:

[see also Equation (8-13)].



Last update: 06/08/2026

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