Substrate-inhibitory analysis of the cholinesterase in the freshwater oligochaete Lumbriculus variegatus (O.F. Műller, 1773; Lumbriculidae, Oligochaeta)

Abstract

Abstract The substrate-inhibitory analysis has shown that single “atypical” cholinesterase (ChE) presents in tissues of freshwater oligochaete Lumbriculus variegatus (O.F. Műller). This enzyme differs both from “typical” acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). Specific activity of oligochaete ChE ranges 55–100 μmol ATCh g−1 tissue min−1 or 0.7–1 μmol ATCh mg−1 protein min−1, ratio of maximal rates (V) of substrate hydrolysises is 100:72:71:83 for acetyl-, propionyl-, butyryl- and acetyl-β-metylthiocholine respectively. Values of Michaelis constant (Km) for these substrates are (1.9–2.5) × 10−4 M. The bimolecular enzyme inhibition rate constants (kII) for organophosphorus inhibitors paraoxon, DDVP, and iso-OMPA are 107, 106 и 103 mol−1 | min−1. ATCh and BuTCh exhibit the effect of substrate inhibition of ChE activity, while PrTCh and MeTCh do not.