M. Ovadia. Isolation and characterization of a hemorrhagic factor from the venom of the snake Atractaspis engaddensis (Atractaspididae). Toxicon 25, 621 - 630, 1987. - The venom of Atractaspis is unique in its composition and contains both high and low molecular weight fractions. The first peak obtained by gel filtration on Sephadex G-50 (S1) induces hemorrhage in the skin of mice. The hemorrhagic activity is stable over a pH range of 6 - 9; at pH 5 or 9.5 the activity decreases to half of the original and it is destroyed when incubated at 56°C for 15 min. The hemorrhagic fraction was further purified by ion exchange chromatography on DEAE-Sepharose followed by ammonium sulphate precipitation. The purified factor had a molecular weight of about 50,000 and, in acrylamide disc electrophoresis, showed an acidic band which strongly stained with Coomassie Brilliant Blue and Periodic Acid Schiff. The specific activity of the isolated hemorrhagin was about 12 times higher than that of the crude venom. It has no measurable protease activity on azocoll, casein or gelatin, but the hemorrhagic activity was inactivated by EDTA and was not restored by prolonged incubation with Ca2+ or Zn2+. This activity was also neutralized by sera of venomous and non-venomous snakes. Moreover, antibodies prepared against the venom of Vipera palaestinae neutralized the activity of Atractaspis hemorrhagin and formed one precipitation line in the immunodiffusion test. It is thus evident that Atractaspis, now considered to belong to a separate family, has a hemorrhagic factor which is similar to that of the venoms of the Viperidae.