Long-lived reactive intermediate photogenerated from N-(5-azido-2-nitrobenzoyl)-N′-(d-biotinyl)-1,2-diaminoethane as an affinity reagent to streptavidin

Irradiation of a complex between N-(5-azido-2-nitrobenzoyl)-N′-(d-biotinyl)-1,2-diaminoethane (I) and streptavidin with light of 313 nm led to the covalent attachment of the photobiotin analogue I to the protein. Streptavidin could also be labelled in the dark with prephotolyzed I. These results indicate that a long-lived reactive intermediate was formed upon irradiation. Moreover, after cleavage of labelled streptavidin with proteinase K this intermediate appears to be covalently attached to the same peptide as the one obtained by direct photoaffinity labelling. An iminosulfurane II derived from the reaction of biotin sulfur atom with aryl nitrene is responsible for the dark-labelling reaction. The photoproduct II converts in an aqueous solution almost completely into N-(5-amino-2-nitrobenzoyl)-N′-(d-(S-oxo)biotinyl)-1,2-diaminoethane (the half-life of II is 10 days).