Properties of some 3-nitrotyrosyl elapid venom cardiotoxins.

Nitration of the invariant Tyr-22 in Hemachatus haemachates cardiotoxin 12B did not greatly decrease lethality, and the haemolytic potency towards guinea-pig erythrocytes remained unchanged. This residue is thus non-essential for cardiotoxin to exert its biological action. Nitration of Naja haje annulifera and Naja melanoleuca cardiotoxins VII1 decreased but did not abolish the lethalities and haemolytic potencies. Thus Tyr-25 and Tyr-51 were concluded to have no direct functional role in cardiotoxin lethality. The pKa values of the phenolic hydroxyl groups of the tyrosine residues appeared to be important for certain properties of cardiotoxin in solution. No evidence could be produced to show that Tyr-51 is unreactive to nitration under normal (non-denaturing) conditions.