Carboxylesterase type B, conserved site Higher eukaryotes have many distinct esterases. Among the different types arethose which act on carboxylic esters (<db_xref db="EC" dbkey="3.1.1"/>). Carboxyl-esterases havebeen classified into three categories (A, B and C) on the basis ofdifferential patterns of inhibition by organophosphates. The sequence of anumber of type-B carboxylesterases indicates [<cite idref="PUB00003630"/>, <cite idref="PUB00004750"/>, <cite idref="PUB00005009"/>] that the majority are evolutionary related. As is the case for lipases and serine proteases, the catalytic apparatus ofesterases involves three residues (catalytic triad): a serine, a glutamate oraspartate and a histidine.<p>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. This entry represents a well conserved site located in the N-terminal section, which contains a cysteine involved in a disulphide bond. Human esterase-D, also a type-B carboxylesterase, does not seem to be evolutionary related. </p>