Gülberk UÇAR*º, Canan TAŞ**

* Hacettepe University, Faculty of Pharmacy, Department of Biochemistry,06100 Sıhhiye, Ankara, TURKEY
**Hacettepe University, Faculty of Science, Department of Biology, 06532 Beytepe, Ankara, TURKEY.
º Corresponding author

Summary:
Scorpion venoms contain a group of neurotoxins which have been shown to interact with ionic channels in excitable membranes and contain some peptides enzymes, amines, and proteases with various effects.In the present study, crude venom of Mesobuthus gibbosus (Buthidae), a scorpion found all over Anatolia axcept on Black Sea shore, was isolated and purified by the Sephadex G-50 gel filtration and high pressure liquid choromatographic (HPLC) separation. Two of the five fractions,obtained from the Sephadex G-50 filtration and derected as lethal on mice and Musca domestica larvae in in vivo toxicity tests were independently subjected to the HPLC separation. Only one of seven fractions obtained from the HPLC saparation of the fraction 5 was found to be extremely lethal sodium dodecly sulfate polyacrylamide gel electrophoretic (SDS-PAGE) analysis of the crude venom and its chromatographic fractions demonstrated that crude venom consisted of peptides with moleculer weights of 6,500-210,000 Da while its neurotoxic fraction appeared as asingle band of 28,000 Da. Two bands of 6,200 and 22,000 Da were determined in SDS-PAGE,respectively,suggesting that it might consist of two chains attached by a disulfide bridge. Crude venom and its neurotoxic fractions obtained from the Sephadex G-50 gel filtration and HPLC separation significantly and specifically inhibited acetylcholinesterase (AchE) in human erythrocytes with the apparent Ki values of 0.90±0.022,0.86±0.017 and 0.78±0.018 mg venom protein/ml, respectively,in a reversible and non-competetive manner. None of the fractions inhibited the butyrylcholinesterase (BchE) of human plasma and erythrocytes. Kinetic data indicated that cholinesterase inhibitory peptides of Mesobuthus gibbosus venom might interact with the enzyme at an alternative binding region possibly close to the peripheral site in the catalytic gorge of the enzyme molecule.

Keywords:
Mesobuthus gibbosus, Buthidae, Acetylcholinesterase, Butyrylcholinesterase, Inhibition.