Carboxylesterase

The enzyme carboxylesterase (or carboxylic-ester hydrolase, EC 3.1.1.1; systematic name carboxylic-ester hydrolase) catalyzes reactions of the following form:


 * a carboxylic ester + H2O $$\rightleftharpoons$$ an alcohol + a carboxylate

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

 * acetylcholinesterase
 * ali-esterase,
 * B-esterase,
 * butyrate esterase,
 * butyryl esterase,
 * carboxylesterase 1
 * carboxylesterase 2
 * carboxylesterase 3
 * esterase A,
 * esterase B,
 * esterase D,
 * methylbutyrase,
 * methylbutyrate esterase,
 * monobutyrase,
 * procaine esterase,
 * propionyl esterase,
 * triacetin esterase,
 * vitamin A esterase, and
 * cocaine esterase

The last enzyme also participates in alkaloid biosynthesis.

Genes
Humans genes that encode carboxylesterase enzymes include:
 * CES1
 * CES2
 * CES3
 * CES4
 * CES7
 * CES8

An approved nomenclature has been established for the five mammalian carboxylesterase gene families.