ABSTRACT
It is possible to modify tyrosyl residues in proteins under relatively mild conditions with reasonably high specificity with a variety of reagents obtaining, in turn, a variety of derivatives. For example,
N
-acetylimidazole (NAI) acetylates the phenolic hydroxyl group in a reversible reaction. Tetranitromethane (TNM) nitrates tyrosyl residues to yield the 3-nitro derivative, which markedly lowers the p
K
of the phenolic hydroxyl group. The 3-nitro function can be reduced under mild conditions to give the 3-amino derivatives, which can be subsequently modified with a variety of useful compounds such as dansyl chloride [5-(dimethylamino)-1-napthalenesulfonyl chloride] or biotinamidonexanoic acid sulfo-
N
-hydroxysuccinimide ester, sodium salt (sulfosuccinimidyl-6-biotinamidohexanoate). Reaction with TNM can also result in zero-length cross-linkage in proteins via the formation of dityrosine.
