Higher eukaryotes have many distinct esterases. Among the different types are
those which act on carboxylic esters (EC 3.1.1.-). Carboxyl-esterases have
been classified into three categories (A, B and C) on the basis of
differential patterns of inhibition by organophosphates. The sequence of a
number of type-B carboxylesterases indicates [1,2,3] that the majority are
evolutionary related. This family currently consists of the following
Acetylcholinesterase (EC 220.127.116.11) (AChE) from vertebrates and from
Mammalian cholinesterase II (butyryl cholinesterase) (EC 18.104.22.168).
Acetylcholinesterase and cholinesterase II are closely related enzymes that
hydrolyze choline esters .
Drosophila esterase 6, produced in the anterior ejaculatory duct of the
male insect reproductive system where it plays an important role in its
Drosophila esterase P.
Culex pipiens (mosquito) esterases B1 and B2.
Myzus persicae (peach-potato aphid) esterases E4 and FE4.
Mammalian bile-salt-activated lipase (BAL) , a multifunctional lipase
which catalyzes fat and vitamin absorption. It is activated by bile salts
in infant intestine where it helps to digest milk fats.
Lipases (EC 22.214.171.124) from the fungi Geotrichum candidum and Candida rugosa.
Caenorhabditis gut esterase (gene ges-1).
Duck acyl-[acyl-carrier protein] hydrolase, medium chain (EC 126.96.36.199), an
enzyme that may be associated with peroxisome proliferation and may play a
role in the production of 3-hydroxy fatty acid diester pheromones.
Membrane enclosed crystal proteins from slime mold. These proteins are,
most probably esterases; the vesicles where they are found have therefore
been termed esterosomes.
So far two bacterial proteins have been found to belong to this family:
Phenmedipham hydrolase (phenylcarbamate hydrolase), an Arthrobacter oxidans
plasmid-encoded enzyme (gene pcd) that degrades the phenylcarbamate
herbicides phenmedipham and desmedipham by hydrolyzing their central
Para-nitrobenzyl esterase from Bacillus subtilis (gene pnbA).
The following proteins, while having lost their catalytic activity, contain a
domain evolutionary related to that of carboxylesterases type-B:
Thyroglobulin (TG), a glycoprotein specific to the thyroid gland, which is
the precursor of the iodinated thyroid hormones thyroxine (T4) and triiodo
Drosophila protein neurotactin (gene nrt) which may mediate or modulate
cell adhesion between embryonic cells during development.
Drosophila protein glutactin (gene glt), whose function is not known.
As is the case for lipases and serine proteases, the catalytic apparatus of
esterases involves three residues (catalytic triad): a serine, a glutamate or
aspartate and a histidine. The sequence around the active site serine is well
conserved and can be used as a signature pattern. As a second signature
pattern, we selected a conserved region located in the N-terminal section and
which contains a cysteine involved in a disulfide bond.
Human esterase-D, also a type-B carboxylesterase, does not seem to be
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