COUPLING AN ALPHA(2)-ADRENERGIC RECEPTOR PEPTIDE TO G-PROTEIN - A NEWPHOTOLABELING AGENT

A photoreactive derivative of a tetradecapeptide G-protein activator ( peptide Q) derived from the alpha(2)-adrenergic receptor was designed and used to label purified G-protein (C-o/G(i)). romoacetyl-N-(3-diazo pyruvoyl)-m-phenylene-diamine (Br-DAP) was conjugated to the C-termina l cysteine of peptide Q. The DAP-modified peptide Q (DAP-Q) specifical ly incorporated into the a subunit of G(o). The incorporation of DAP-Q into alpha(o) was blocked by unmodified Q peptide (IC50 = 15 +/- 6 mu M; n = 4). Photolysis of sixfold higher concentrations of DAP-Q with ovalbumin or bovine albumin failed to produce cross-linked products. B r-DAP should prove useful in detecting mutual contact sites between pe ptides and their binding proteins.