Effect of modification of tyrosine residues in cytotoxin-1 from Indian cobra venom. (Naja naja naja).

The role of tyrosine residues in the biological activity of cytotoxin-1 was evaluated using N-bromo succinimide. N-bromo succinimide effected the oxidation of tyrosine residues in cytotoxin-1 with an increase in absorption at 260 nm. N-chloro succinimide was ineffective in the oxidation of tyrosine residues in the toxin. Oxidation of a single tyrosine residue (at 3.50 equivalents of N-bromo succinimide/mole of the toxin) resulted in complete loss of lethal activity of the toxin. The lytic activity of the toxin (lysis of erythrocytes) remained uneffected even after three of the four tyrosine residues in the toxin were oxidised.