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 (Ki = 22.9 nM) for [125I]IAPP binding and rat alpha CGRP (Ki = 0.904 nM) had a higher affinity for [125I]CGRP binding over related peptides. [125I]IAPP binding was unaffected by GTP gamma S, 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.