Photoinactivation and identification of the biogenic amine transporter in chromaffin granules from bovine adrenal medulla.

We have synthesized a new derivative of 5-hydroxytryptamine, a substrate of the biogenic amine transporter in bovine chromaffin granules. This new compound, 4-azido,3-nitrophenyl-azo-(5-hydroxytryptamine), is a competitive, reversible, and specific inhibitor of the biogenic amine transporter in the dark (Ki = 2 microM)., Upon illumination, the inactivation of the transporter becomes irreversible and follows an apparent first order rate kinetics (KINAC = 4 microM). The transporter can be protected if other substrates are present during illumination. When [3H]4-azido,3-nitrophenyl-azo-(5-hydroxytryptamine) is used, preferential labeling of one polypeptide (Mr approximately 45,000) is observed in the light, provided no other substrates of the transporter are present during illumination. We have tentatively identified this polypeptide as the transporter itself or one of its subunits.