The effects of buffer diffusion on the activity of an immobilized esterase

In vitro study of organophosphorus inactivators of membrane acetylcholinesterase and of reactivating pyridinium-oximes using rat brain slices

A modified method of Ellman's reaction with a continuous flow was used to study the cerebral cholinesterase activity in its biological environment with rat brain slices including the striatum. Comparative studies were performed under various conditions of flow and substrate concentrations (acetylthiocholine bromide) and with or without formaldehyde fixation. We could thus measure either the inhibition rate of cerebral ChE by paraoxon or MPT or the reactivation rate by some oximes in the presence of substrate and after removing excess inhibitor.

Effects of carrier morphology and buffer diffusion on the expression of enzymatic activity

A very stable esterase (EC 3.1.1.-), which hydrolyses ethyl acetate, cephalosporin C and other acetyl esters with a maximum turnover number of 3-10(2) s-1, was isolated from Bacillus subtilis ATCC 6633 and immobilized on two supports: controlled-pore glass and powdered brick, a representative of carriers having a wide pore-size distribution. Carrier morphology determines diffusion rates and the expression of activity. Rate-limiting mass transfer of buffer leads to apparent losses of activity, gross distortions of molecular pH vs. activity profiles and to apparent deviations from Michaelis-Menten kinetics.