Effect of Calcium on the Hydrolysis Activity of Human Butyrylcholinesterase.

The aim of this experiment was to study the effects of calcium ion on the hydrolysis of cationic and anionic substrate by human butyrylcholinesterase (HuBChE). The hydrolysis of aspirin, an anionic substrate, by HuBChE was markedly increased in the presence of increasing concentrations of calcium ion (∼20 mM), as shown by the increasing k (∼18-fold). Butyrylthiocholine (BTC), a cationic substrate, was biphasically hydrolyzed with substrate activation; a second BTC molecule caused a 3-fold increase in k.

Aspirin hydrolysis in human and experimental animal plasma and the effect of metal cations on hydrolase activities.

The hydrolyzing properties of plasma esterases for aspirin were investigated in human plasma and plasma from experimental animals. The observed rates of aspirin hydrolysis were in the following order: rabbit > human > monkey > rat > mouse > dog > minipig. In human, monkey, and dog plasma, aspirin was hydrolyzed by their major hydrolases, paraoxonase (PON), butyrylcholinesterase (BChE), and albumin.

Species difference of esterase expression and hydrolase activity in plasma.

Differences in esterase expression among human, rhesus monkey, cynomolgus monkey, dog, minipig, rabbit, rat, and mouse plasma were identified using native polyacrylamide gel electrophoresis. Paraoxonase (PON) and butyrylcholinesterase (BChE) were ubiquitous in all species, but were highly expressed in primates and dogs, whereas carboxylesterase (CES) was only abundant in rabbits, mice, and rats. Several unknown esterases were observed in minipig and mouse plasma.