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Acetylcholinesterase (AChE) was investigated in Walterinnesia aegyptia venom and characterized with respect to its kinetic properties. It was found that 4.0 ug of crude venom protein and an incubation time of 4.0 min were suitable conditions for linearity of AChE activity at 25 degrees C. The optimum strength of the sodium phosphate buffer was 0.05 M, and the optimum pH was 7.75. The optimum temperature was 30 degrees C. The activation energy and the heat of activation were observed to be 6510 and 5922 cal/mole. The AChE was specific for acetylthiocholine but it did not hydrolyse butyrylthiocholine. The optimum substrate concentration was 3.0 mM but at higher substrate concentrations, the AChE activity declined. The ASCh concentration ranges for different orders of the reactions were determined and kinetic parameters (K-m, V-max, k(cat), and k(sp)) were established at each order of the reaction.