Immunocytochemical characterization of clathrin-associated proteins (CAPs). II. Immunolocalization of CAPs using selectively-absorbed IgG solutions.

Utilizing antibodies elicited by clathrin-associated proteins (CAPs) absorbed with three different antigenic states of CAPs, i.e., bound to clathrin (clathrin-CAPs complex), free in solution (CAPs) or partially cleaved by chymotrypsin (CAPs-subfragments), indicated that when CAPs are bound to clathrin an antigenic site (or sites) remain(s) unexposed and CAPs-subfragments lose antigenic sites as a result of limited proteolysis. IgG remaining in solution after absorption with CAPs-subfragments were directed against the chymotrypsin-sensitive, or accessible portions of CAPs, whereas IgG remaining after absorption with clathrin-CAPs complex were directed against the unexposed antigenic site(s) characteristic of the clathrin-CAPs complex. Immunocytochemical characterization of these selectively-absorbed IgG solutions suggests that CAPs detected during immunolocalization exist as a complex with clathrin.