IDENTIFICATION OF VASOACTIVE INTESTINAL POLYPEPTIDE (VIP) BINDING-PROTEIN IN BOVINE PINEAL-GLAND

Vasoactive intestinal polypeptide (VIP) containing nerves are present in close proximity to epithelial, endocrine, and vascular smooth muscl e cells. The pineal gland, known also as a ''neuroendocrine transducer organ'' contains a high content of VIP which prompted us to character ize the binding sites for VIP in this organ. [Tyr10-I-125]VIP was boun d selectively and specifically to pineal membrane preparations in a ti me-dependent fashion. Scatchard analysis demonstrated a single class o f high affinity binding sites with a dissociation constant (K(d)) valu e of 5.7+/-0.52 nmol/l and a receptor density (B(max)) value of 440+/- 35 fmol/mg protein. A Hill Plot with a slope of 1.013 indicated the ab sence of cooperativity. Covalent crosslinking with [Tyr10-I-125]VIP fo llowed by SDS electrophoresis and autoradiography, revealed that the V IP binding protein exhibited a molecular weight of 51.8+/-0.5 kDa. The precise function of pineal VIP binding protein remains to be delineat ed.