5-Isothiocyanato-1-naphthalene azide and rho-azidophenylisothiocyanate. Synthesis and application in hydrophobic heterobifunctional photoactive cross-linking of membrane proteins.

Two hydrophobic, heterobifunctional azidoarylisothiocyanates have been synthesized. The reagents are applicable for group-directed modification of membrane-integrated protein segments and subsequent photo-induced cross-linking with neighbouring membrane constituents. Both 5-isothiocyanato-1-naphthalene azide and p-azidophenylisothiocyanate are chemically characterized with respect to structure and photosensitivity. The reagents compete for the documented phenylisothiocyanate binding site(s) in bacteriorhodopsin and to the anion-exchange protein (band 3) of human erythrocytes. Photoactivation of azidoarylisothiocyanate-labeled membrane proteins leads to homopolymers when cross-linked in purple membranes or in vesicles enriched in the anion-exchange protein.