Cholinesterases common features

B-esterases are the group of enzymes that can be inhibited by organophos-phorus compounds in the reaction that is time- and temperature-dependent. This group of enzymes comprises CarbE, AChE (EC 3.1.1.7), serum cholinesterase (ChE EC 3.1.1.8), chymotrypsin, trypsin and some other enzymes. A common feature of these enzymes is that they have serine hydroxyl group at the active site that enables them to react with OPC in the similar fashion (Figure 3). From the... 

The human lysosmal serine carboxypeptidase CatA is a member of the a/p hydrolase enzyme family and therefore shares structural homology with yeast carboxypeptidase Y and cholinesterases [4] (Figure 23.1). The common feature shared by members of this family is a three-dimensional structure of eight p sheets connected by a-heUces resulting in a typical topological localization of the catalytic triad, in which only the His residue is conserved [2]. 

Fig. 11.2. Schematic representation of the primary structure of secreted AChE B of N. brasiliensis in comparison with that of Torpedo californica, for which the three-dimensional structure has been resolved. The residues in the catalytic triad (Ser-His-Glu) are depicted with an asterisk, and the position of cysteine residues and the predicted intramolecular disulphide bonding pattern common to cholinesterases is indicated. An insertion of 17 amino acids relative to the Torpedo sequence, which would predict a novel loop at the molecular surface, is marked with a black box. The 14 aromatic residues lining the active-site gorge of the Torpedo enzyme are illustrated. Identical residues in the nematode enzyme are indicated in plain text, conservative substitutions are boxed, and non-conservative substitutions are circled. The amino acid sequence of AChE C is 90% identical to AChE B, and differs only in the features illustrated in that Thr-70 is substituted by Ser.

Many workers in the organo phosphorus field have from time to time suggested theories to explain anti cholinesterase activity.1 These theories differ in certain respects, but some features are common to them all. Nothing, however, can be at all certain until pure cholinesterase has been obtained. 

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