BChE enzyme interactions with

The detailed mechanism by which AChE and BChE hydrolyze ACh has been the subject of much research, especially since the crystal structure of the Torpedo califomica AChE was elucidated by Sussman et al. in 1991 [12]. (Reviews of these enzymes and their interactions can be found in Refs. [5,13]). This mechanism will be described here only briefly, as an introduction to the reaction of the enzyme with carbamates. The active site of AChE is located at the bottom of a 20 A-deep gorge, where acetylcholine fits in by attachment of the quaternary ammonium group to the so-called anionic site (mainly through cation interaction with the n electrons of Trp84), and by dipole interactions between the ester group and Ser200 at the esteratic site . 

Since the enzyme is likely attached to the polymer at multiple points and therefore becomes partially distorted, it is not unexpected that the values for the immobilized ChE and OPH were about 10-fold greater than for the corresponding soluble enzyme, but the combined effects on affinity for substrate and k j resulted in approximately a 20- to 50-fold decrease in acylation (k. (/K ). Yet there was no observed shift in the pH profile of the enzymes, and, more important, the bimolecular rate constants for the inhibition of AChE-sponge and BChE-sponge and the soluble enzymes by MEPQ showed no significant difference between soluble and covalently bound enzymes. Therefore, the OP interacts similarly with soluble and immobilized ChE. 

Sensor systems based on the reversible, competitive inhibition of AChE and BChE by monosulfonate tetraphenyl porphyrin (TPPSi) were developed. TPPSi (350 iM in 50 mM pH 7 NaPi with 25% edianol) was applied to surfaces of immobilized enzymes and allowed to interact for 20 min before rinsing the excess solution off with excess buffer (50 mM NaPi pH 7). TPPSi was found to be a competitive inhibitor of cholinesterase activity for both AChE and BChE 12, 14, 15). The absorbance spectrum was unique for the AChE-TPPS complex (TAC) as compared to that of the BChE-TPPSi complex (TBC) with characteristic peaks at 446 nm for TAC and 412 nm for TBC. When TPPSi was applied to a siuface bearing both AChE and BChE (TABC), the characteristic peaks for both TAC and TBC were observed in the absorbance spectrum. 

---