Indophenol Chromogenic Substrates of Cholinesterases of Different Origin

An analysis of influence of indophenol substrate structure on rate of their enzymatic hydrolysis under action of cholinesterases (ChE) of different animals is carried out for the first time. Study of indophenylacetate (IPhA) and a group of isomeric dichloroderivatives as substrates of erythrocyte acetylcholinesterase, serum butyrylcholinesterase, and ChE from optical ganglia of the Pacific squid Todarodes pacificus allowed us to reveal a role of steric and inductive effects of the substrates molecule in enzymatic catalysis, as well as differences in substrate specificity of the studied ChE. This comparative enzymologic aspect of the work was evident to a greater degree at studying hydrolysis of choline (acetylcholine, acetylthiocholine) and indophenol (IPhA, 2,6-dichloroindophenylacetate, 2,6-dichloro-3´-methyl indophenylacetate) esters under action of mammalian blood ChEs, ChE from hemolymph of the gastropod mollusc Neptunea, and also of ChE from the nervous tissue of different species of Pacific squids and of the cabbage root fly. Differences in values of the kinetic parameters characterizing sorption and catalytic stages of the hydrolysis process are revealed. Comparison of substrate properties of choline and indophenol esters enabled us to compare enzymes in terms of hydrophobic-hydrophilic interactions.