Specific binding of synthetic human pancreatic growth hormone releasing factor (1–40-OH) to bovine anterior pituitaries

Abstract

We have studied the specific binding of a synthetic 40 amino acid, free carboxy terminus analog of human pancreatic growth hormone releasing factor (hpGRE-40-OH) to partially purified homogenates of bovine anterior pituitaries. The binding of hpGRF-40-OH to pituitary receptors at 4°C reached maximal level in 4 hours and remained steady for the next 18 hours. Specific binding increased linearly with the amount of protein present in the assay. 125I-hpGRF-40-OH binding to pituitary homogenates was competitively inhibited by hpGRE-40-OH but not by unrelated hormones. The competition curve and Scatchard analysis suggest the presence of single class of receptors with a K d⋍3nM and binding capacity of ≈200 fmoles/mg protein. This is the first demonstration of specific receptors for GRF on anterior pituitary cells.