Chemical modifications of tyrosyl residue(s) and action of human-fibroblast interferon

Partially purified and purified human fibroblastoid interferon were iodinated and nitrated under experimental conditions in which the most likely amino acyl residue modified was tyrosine(s). The modification resulted in a loss of human interferon activity suggesting that tyrosyl residue(s) is associated with the antiviral action of human interferon.