Overwhelming amount of heavy metals discharged due to industrialization is a serious global concern. Thus, an investigation was done on acetylcholinesterase (AChE) from Asian swamp eel, Monopterus albus, as an alternative biosensor to detect various metal ions. AChE from the brain of M. albus was purified through ammonium sulphate precipitation and procainamide affinity chromatography. Enzyme recovery was obtained at 38.73% with the specific activity of 1847 U μg−1. The Michaelis constant (Km) value and maximal velocity (Vmax) were determined at 8.910 mM and 29.44 μmol min−1 mg−1, respectively for acetylthiocholine iodide (ATC). Based on effective coefficient ratio, AChE from M. albus brain showed higher affinity to ATC compared to butyrylthiocholine iodide (BTC) and propionylthiocholine iodide (PTC) at the value of 3.304, 1.515, 2.965 Vmax.Km−1 respectively. Optimum activity of AChE was obtained at 40°C and incubated in 0.1M Tris HCl buffer pH 9.0. Inhibition study performed on 10 heavy metals resulted in this descending order of inhibition mercury<chromium<zinc<copper<arsenic<silver<cobalt<cadmium<lead<nickel, with mercury and chromium showing more than 50% inhibition at 10 ppm. Data from this study can be further utilized to develop a cheaper, easier, and faster heavy metal detection method as compared to conventional methods available.

Heavy metals pollution has now become a serious environmental problem worldwide especially in Malaysia River. As a precaution, continuous environmental monitoring is needed to minimize heavy metal to the ecosystem. Inhibitive enzyme assay based on enzyme including cholinesterase has been introduced as a rapid, cheap and reliable method to assess the level of contamination in the river. In this study, the Asian swamp eel, Monopterus albus, was selected and determined of the sensitivity level towards heavy metals. The liver of M. albus was extracted and purified using ion exchange chromatography of which DEAE sepharose as the matrix of the column. Based on the Ellman assay, cholinesterase was obtained at 4.86 purification fold with the percentage recovery of 30.32 %. The enzyme works optimally at pH 9 (0.1 M Tris-HCl buffer) and 25 °C, while BTC; 369×103 U.mg−1 was selected as the preferable substrate which shows highest catalytic efficiencies compared to ATC and BTC at 1457 × 103, 1220 × 103 and 488 × 103 Vmax.Km−1, respectively, Cholinesterase was tested with eight metal ions at the concentration of 5 ppm and the ascending order of inhibition is as followed; arsenic = chromium ⩽ plumbum ⩽ copper ⩽ argentum = nickel < mercury. From this study, the ability of cholinesterase partially purified from the liver tissue of M. albus has the potential to be an assay for heavy metals.

Affinity chromatography for acetylcholinesterase; AChE namely Procainamide Sepharose CL-6B was synthesised through the coupling method between soluble procainamide hydrochloride immobilised by a cross-linked agarose size exclusion, sepharose CL-6B. 1, 4-butanediol diglycidyl ether plays a role in building up a productive and rigid connecting of a biospecific ligand (Procainamide hydrochloride) to an insoluble matrix (Sephacryl CL-6B). Local freshwater eel brain was extracted and centrifuge at high speed. The supernatant was collected, and seven different volumes were separately loaded on to the column for isocratic purification where 12 fractions were collected at the end of elution stage. This study shows 1000 μL of extractant; considered as the maximum volume to load onto the column. Lastly, a stepwise elution was performed with five different concentrations of NaCl, and each of 1 mL fraction was collected then assay for determination of enzyme activity and protein content. The data shows AChE was successfully purified with percentage recovery of 38 % after 21 purification fold. Kinetic study strengthens the data where the efficient coefficient ratio of ATCi was much higher compared to PTCi and BTCi at 3.03, 2.67 and 1.52 Vmax⋅Km −1, respectively, prove that the collected fraction predominantly contained with AChE, which is a targeted enzyme to be used as a sensitive biosensor to detect the presence of carbamate and organophosphate contamination in the environment.

Development in Malaysia is in line with positive economic growth. The situations have led to the improvement of industrial and agricultural activities that produce high-quality products of a global quality, which has a significant impact on the income of the local people. However, the activity also contributed to river pollution, where the industrial and agricultural wastes were discharged to nearby water sources, whether intentionally or not. The residues containing heavy metals are of concern because their concentration can negatively affect the environment. Furthermore, their ability to be treated or remedied is very limited. Biosensor acetylcholine, AChE extracted and purified from Monopterus albus brain, acts as an alternative biosensor to rapidly detect the presence of heavy metals with a simple application. The tests were conducted at ten different location points from the upstream to the downstream of Bentong River and Terengganu River, classified as a Class II river by the Department of Environment Malaysia. Bentong River and Terengganu River showed that five and two samples from different location points were able to inhibit AChE activity by more than 10%, respectively. The three samples with the highest inhibition were selected for the secondary screening through identification and the heavy metal concentrations determination using ICP-OES. All samples showed heavy metals such as copper, nickel, lead, arsenic, silver, chromium, and zinc at different concentrations and synergistically affected AChE activity. The use of AChE as a biosensor is able to detect and characterize pollution levels in both rivers that differ in the level of local development, such as industrial activities and population density.