Dual labeled peptides as tools to study receptors: Nanomolar affinity derivatives of TIPP (Tyr-Tic-Phe-Phe) containing an affinity label and biotin as probes of δ opioid receptors

A general strategy for the design of dual labeled peptides was developed, and derivatives of the δ opioid receptor (DOR) selective antagonist TIPP (Tyr-Tic-Phe-PheOH) containing both an affinity label and biotin were prepared by solid-phase synthesis. Tyr-Tic-Phe-Phe(p-X)-Asp-NH(CH₂CH ₂O)₂-CH₂CH₂NH-biotin (where X = N=C=S or NHCOCH₂Br) exhibit nanomolar DOR affinity. The ability to detect receptors labeled with these peptides following solubilization and SDS-PAGE demonstrate the applicability of this design approach for dual labeled peptide derivatives.