Characterization of the receptor to vasculotropin on bovine adrenal cortex-derived capillary endothelial cells

Recently a new growth factor was purified to homogeneity, and its bioactivity seemed to be restricted to vascular endothelial derived cells. As it was also angiogenic in vivo, it was provisionally named vasculotropin (VAS). As an iodination procedure used to label VAS did not damage the molecule, it was possible to undertake binding studies. The binding of iodinated vasculotropin to bovine adrenal cortex-derived capillary endothelial cells was saturable at 250 pM, and half-maximal binding occurred at 47 pM. Scatchard's analysis of the data demonstrated two apparent classes of binding sites with apparent dissociation constants of 2 and 82 pM displaying 280 and 3400 binding sites, respectively. The binding was specific; half-displacement was observed with a 2-fold excess of unlabeled VAS. The structurally related platelet-derived growth factor did not compete in a radioreceptor assay. 125I-VAS was displaced by suramin and not by heparin. 125I-VAS was covalently cross-linked to its cell surface receptor on intact bovine adrenal cortex-derived capillary endothelial cells using the homobifunctional agents ethylene glycol bis(succinimidyl succinate) or disuccinimidyl tartarate. A major macromolecular species with an apparent molecular mass of 230,000 Da was labeled under reducing and nonreducing conditions. These data demonstrate the existence of a specific binding protein for VAS and an estimation of the size at 185,000 Da.