Solubilization of binding sites for IAPP and CGRP from rat lung

Functional binding sites for ¹²⁵I]IAPP and ¹²⁵I]CGRP were solubilized from rat lung membranes with CHAPSO (10 mM). Rat IAPP had a higher affinity (K_i = 22.9 nM) for ¹²⁵I]IAPP binding and rat CGRP (K_i = 0.904 nM) had a higher affinity for ¹²⁵I]CGRP binding over related peptides. ¹²⁵I]IAPP binding was unaffected by GTPγS, but ¹²⁵I]CGRP binding was 50% inhibited, indicating solubilization of a G-protein-receptor complex for CGRP but not IAPP binding. Wheat germ agglutinin affinity columns gave a 25-fold purification of IAPP binding sites, but no CGRP binding sites were eluted from the column, indicating different patterns of glycosylation of the two sites.