Specific water-soluble binding sites for serum insulin-like peptides in human and animal tissues.

Abstract

The cytosol fraction of rat liver and kidney and human placenta was shown to possess soluble binding proteins for an insulin-like somatomedin peptide (ILAs). A similar component was also found in the cytosol fraction of livers and kidneys from guinea pigs, rabbits, and dogs. Assessment of binding was performed by gel filtration on Sephadex in 25 mm Tris-HCl, pH 7.4, or by dextran-coated charcoal separation. Specific binding of [l25I]iodo-ILAs was shown, at 4 C in vitro, to reach equilibrium by 4 h. Specific binding was reduced and degradation of [l25I]iodo-ILAs was increased when incubations of rat liver and kidney cytosol preparations were carried out at 37 C. Cytosol binding of [l25I]iodo-ILAs was specifically inhibited by unlabeled ILAs but not by insulin, human GH, nerve growth factor, or epidermal growth factor even at concentrations of 1 μg/ml. Specific binding of [l25I]iodo-ILAs was shown to increase linearly as a function of cytosol concentration used and was consistently greatest in human placent...