Some exceptions include an esterase with β-lactamase-like structure (PDB: 1ci8).
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.
[2] 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.
Humans genes that encode carboxylesterase enzymes include: An approved nomenclature has been established for the five mammalian carboxylesterase gene families.