| abstract |
Polypeptide compositions are provided having a binding site specific for a particular target ligand and further having an active functionality proximate the binding site. The active functionality may be a reporter molecule, in which case the polypeptide compositions are useful in performing assays for the target ligand. Alternatively, the active functionality may be a chemotherapeutic agent, in which case the polypeptide compositions are useful for therapeutic treatment of various diseased states. A novel method for preparing such polypeptides having active functionalities proximate their binding site comprises combining the polypeptide specific for the target ligand with an affinity label including ligand having a reactive group attached thereto. The reactive group is then covalently attached to an amino acid side chain proximate the binding site and cleaved from the substrate. The substrate is eluted, leaving a moiety of the reactive group covalently attached to the polypeptide. The active functionality may then be attached to the moiety. |