The enzyme carboxylesterase (or carboxylic-ester hydrolase, EC 3.1.1.1; systematic name carboxylic-ester hydrolase) catalyzes reactions of the following form: Most enzymes from this group are serine hydrolases belonging to the superfamily of proteins with α/β hydrolase fold. Some exceptions include an esterase with β-lactamase-like structure. Carboxylesterases are widely distributed in nature, and are common in mammalian liver. Many participate in phase I metabolism of xenobiotics such as toxins or drugs; the resulting carboxylates are then conjugated by other enzymes to increase solubility and eventually excreted. The essential polyunsaturated fatty acid arachidonic acid (AA C20H32O2; 20:4, n-6), formed by the synthesis from dietary linoleic acid (LA: C18H32O2 18:2, n-6), has a role as a human carboxylesterase inhibitor. The carboxylesterase family of evolutionarily related proteins (those with clear sequence homology to each other) includes a number of proteins with different substrate specificities, such as acetylcholinesterases.

Examples

The last enzyme also participates in alkaloid biosynthesis.

Genes

Humans genes that encode carboxylesterase enzymes include: An approved nomenclature has been established for the five mammalian carboxylesterase gene families.