The Effect of Selective Modification of Tryptophan, Lysine and Arginine Residues of Basic Brain Protein on Encephalitogenic Activity

Abstract

Basic protein (BP), which caused experimental allergic encephalomyelitis in guinea pigs in a dose of 30 μg, was isolated from bovine brain. Studies were carried out to characterize the encephalitogenic determinant by means of selective and permanent modification of tryptophan, lysine and arginine residues of BP. When tryptophan residues of BP were altered by the addition of 0.045 μmol 2-hydroxy-5-nitrobenzyl bromide/mg BP, preparations exhibited a significant decrease in encephalitogenic activity. In contrast, acetylation of free amino groups of lysine with acetic anhydride, or modification of guanidinium groups of arginine with 2,3-butanedione, had no effect on the encephalitogenic activity of BP. These results suggest that tryptophan is an essential component of the encephalitogenic determinant, whereas lysine and arginine are probably not present in this site.