1968 Volume 59 Issue 3 Pages 231-238
In order to obtain information on the site of amino acid binding in the polar dyes, investigations were made with polar dyes derived from 3, 5-dimethyl-4-(dimethylamino)azobenzene (I) and 4-amino-2', 3-dimethylazobenzene (II). It was found that both (I) and (II) can give rise to appreciable amounts of proteinbound dyes in spite of the facts that (I) has methyl substitutions at both 3 and 5 positions and (II) lacks an N-methyl group. The polar dyes from (I) and (II) gave evidence indicating the presence of S-containing amino acid (probably methionine) residue and of 4-amino group of a secondary type. Both polar dyes gave non-polar dyes having a primary auxochromic amino group by prolonged alkaline treatment. It was postulated that the amino acid residue may be bound to the azo dye at the site of 4-amino nitrogen in the cases of (I) and (II). On the other hand, the polar dyes derived from DAB or 3'-methyl-DAB gave non-polar dye having a secondary auxochromic amino group as major products by alkaline treatment.
