This study reports on the characterization of a purified AChE from Oreochromis mossambica
brain extract. The purification protocol involved the application of custom-synthesized affinity
chromatography gel (Edrophonium–Sephacryl S-400) and the use of high performance liquid
chromatography system (HPLC). Soluble AChE was partially purified 27.9 fold with a highest
specific activity around 73.1 × 103 U/mg proteins. The partially purified AChE higher capability
to hydrolyse acetylthiocholine (ATC) and shows less degradation against propionylthiocholine
(PTC) and also butyrylthiocholine (BTC). Based on enzyme kinetic analysis, the partially
purified AChE exhibits the apparent Michaelis constants Km, for ATC, PTC and BTC in the
range of 125, 260 and 600 μM and the maximum velocities Vmax were 276, 59 and 36
μmol/min/mg protein, respectively. The apparent inhibition constant (ki) values of eserine,
propidium and carbofuran were 0.24 μM-1min-1, 65 μM-1min-1 and 0.41 μM-1min-1 μM-1min-1,
respectively. The purified enzyme is apparently an AChE since it capable to hydrolyzes ATC at a
higher rate compared to other synthetic substrates, at pH 7.0 and 25ºC, and is inhibited by it
specific inhibitor which is eserine but not by iso-OMPA.
Acetylcholinesterase (AChE) is usually used as an inhibitive assay for insecticides. A lesserknown
property of AChE is its inhibition by heavy metals. In this work, we evaluate an AChE
from brains of Clarias batrachus (catfish) exposed to wastes from aquaculture industry as an
inhibitive assay for heavy metals. We discovered that the AChE was inhibited completely by
Hg2+, Ag2+, Pb2+, Cu2+, Cd2+, Cr6+ and Zn2+ during initial screening. When tested at various
concentrations, the heavy metals exhibited exponential decay type inhibition curves. The
calculated IC50 (mg/L) for the heavy metals Ag2+, Cu2+, Hg2+, Cr6+ and Cd2+ were 0.088, 0.078,
0.071, 0.87 and 0.913, respectively. The IC50 for these heavy metals are comparable, and some
are lower than the IC50 values from the cholinesterases from previously studied fish. The assay
can be carried out in less than 30 minutes at ambient temperature.
In this work we assess the potential of acetylcholinesterase (AChE) from Oreochromis
mossambicus (Toman) as a sensitive test for the presence of insecticides. The partial purification
and characterization of a soluble AChE from Oreochromis mossambicus brain tissues using
affinity chromatography gel (procainamide–Sephacryl S-1000) showed that the partially purified
AChE was most active on acetylthiocholine (ATC) but had low activities on
propionylthiocholine (PTC) and butyrylthiocholine (BTC), indicating that the partially purified
fraction was predominantly AChE. Soluble AChE was partially purified 9.27-fold with a 91.12%
yield. The partially purified AChE displayed the highest activity on ATC at pH 7 and at 30oC
using 0.1 M Tris buffer. The enzyme exhibited Michaelis-Menten kinetic constants, Km, for
ATC, BTC and PTC at 36, 77 and 250 μM, respectively, and the maximum velocities, Vmax, were
18.75, 0.12 and 0.05 μmol/min/mg protein, respectively. Moreover, the AChE from
Oreochromis mossambicus presented comparable sensitivity to carbamates and
organophosphates insecticides than that from Electrophorus electricus and many other fish
AChE by comparing half maximal inhibitory concentration values. Therefore, the enzyme is a
valuable source for insecticides detection in Malaysian waters at lower cost.