engleski

Interaction of wild type horse serum butyrylcholinesterase with ethopropazine

Kinetic behaviour of cholinesterases deviate from Michaelis-Menten pattern. An apparent activation is observed at low substrate concentrations and almost complete inhibition can be measured at the highest applicable substrate concentrations. One or the other phenomenon, however, is lacking in enzymes from various sources and under different experimental conditions. It has long been believed that butyrylcholinesterases lack inhibition by the excess of substrate but detailed analysis confirmed moderate decrease of the activity at butyrtythiocholine concentrations approaching solubility maximum. In order to elucidate exactly this point, we investigated the action of ethopropazine, a reversible peripheral ligand, on wild type butyrylcholinesterase from Horse serum at 250C and 370C. The results of the kinetic analysis of the data obtained on a stopped-flow apparatus revealed relative temperature independence of kinetic parameters reflecting substrate turnover. The shape of pS curves at 370C show no inhibition at high substrate concentrations but the analysis of data in the presence of the inhibitor suggests that the loss in substrate and ethopropazine affinities at 370C could be responsible. Additionally, partial competitive reaction mechanism between the substrate and the first inhibitor molecule at the peripheral anionic site turned to the complete inhibition by the binding of the second ethopropazine molecule at 250C. All these suggest that upon binding ethopropazine induces fast conformational changes in Horse serum butyrylcholinesterase which are facilitated at higher temperatures.

nije evidentirano

nije evidentirano