Occurrence of a unique protein toxin from the Indian King Cobra (Ophiophagus hannah) venom

A unique (lethal-cardiotoxic-hemorrhagic) protein toxin (Toxin CM55) was isolated and purified from Indian King Cobra (Ophiophagus hannah) venom by CM-sephadex ion exchange chromatography and reverse phase HPLC. The purified toxin had an SDS-molecular weight of 22 +/- 0.5 kD. UV absorption spectra of Toxin CM55 showed a peak at 280 nm, whereas when excited at 280 nm fluorescence, Toxin CM55 showed an E-max at 333.4 nm. Toxin CM55 had an LD50 of 28.28 mu g/20 g (i.v.) in albino mice. The cardiotoxic action of the toxin was established on isolated guinea pig/rabbit heart and guinea pig auricle. In rats, Toxin CM55 caused ECG abnormalities including widened QRS complex and monomorphic ventricular tachycardia suggesting that the possible site of action of Toxin CM55 was the ventricle. Toxin CM55 produced significant vasoconstriction on peripheral blood vessels. It produced significant contraction of isolated guinea pig ileum, rat fundus and rat uterus, which was completely antagonised by methysergide. The toxin was found to release a significant amount of serotonin from rabbit platelets. Toxin CM55 produced cutaneous hemorrhage in albino mice, which was also produced in reserpine and p-chloro phenylalanine pretreated animals. Rabbit antiserum was raised against Toxin CM55, which gave prominent bands in immunogel diffusion and immunoelectrophoresis. The antiserum provided 2 LD50 protection against Toxin CM55-induced lethality in mice and also neutralised 3 MHD hemorrhagic dose of the toxin. (C) 2000 Elsevier Science Ltd. All rights reserved.