Chemical modification of mouse interferons

Mouse interferon (MuIFN) preparations containing both the alpha and beta species were treated with chemical modifying reagents specific for lysine, cysteine and tryptophan residues. The purpose was to ascertain whether reagents which modify specific amino acid residues distinguished MuIFN-alpha from MuIFN-beta, and if biologic properties could be correlated with specific amino acid residues. MuIFN species were characterized by their activity on homologous and heterologous cells and by antibody neutralization. Modification of lysine residues with increasing concentrations of fluorescamine resulted in a concomitant loss of biologic and antigenic activities of both MuIFN species. Modification of cysteine residues with 5,5'-dithio-bis (2-nitrobenzoic acid) showed an enhancement of antiviral activity of MuIFN-alpha but a gradual decrease in all activities of MuIFN-beta. Modification of tryptophan residues with 2-methoxy-5-nitrobenzyl bromide enhanced somewhat MuIFN-alpha activity, but resulted in the loss of MuIFN-beta activity. These results show that amino-modifying reagents rendered both major species of MuIFN inactive; however, they can be distinguished by reagents which affect cysteine and tryptophan residues. The fact that biologic activity is accompanied by the loss of antigenicity implies that the biologic and antigenic sites may be the same or closely associated. Chemical modification of interferons may provide a useful approach for relating the properties of interferons to their primary structure.