Radiolabeling of receptor ligands by chemical incorporation of phosphorylation sites

A chemical reagent, N-acetyl-cys((succinimidyl-6-(thioacetyl)amino) hexanoate)-ser-arg-arg-ala-ser-val-tyr-amide ("phosite NHS ester"), allowing the introduction of phosphorylation sites into proteins, peptides, or small molecules, has been synthesized and characterized. The phosite reagent enables the enzymatic radiolabeling of any protein, peptide, or small molecule containing a reactive amine using [P-32] or [P-33]ATP and protein kinase A. The utility of the reagent has been demonstrated in cytokine and G protein-coupled radioligand receptor binding assays using whole cell and immobilized receptor formats. Use of the reagent does not require genetic manipulation of the target ligand. (C) 1999 Academic Press.