Evidence for presence of proinsulin-immunoreactive glycoprotein(s) in fetal bovine pancreatic extracts.

A large-molecular-weight proinsulin-immunoreactive protein fraction was obtained from an extract of fetal bovine pancreases by gel filtration in 6 M guanidine-1 M acetic acid. Concanavalin A-Sepharose-affinity column chromatography of the large-molecular-weight fraction yielded a discrete alpha-methyl-mannoside-displaceable immunoreactive peak that also displayed N-acetylglucosamine-specific binding to wheat germ lectin-Sepharose. Chemically tritiated and radioiodinated lectin-reactive proteins interacted specifically with antibodies to insulin and bovine proinsulin. Immunochemically purified (reaction with antibodies followed by separation of antigen-antibody complexes on protein A-Sepharose) radiolabeled lectin-reactive proteins were analyzed by gel filtration in guanidine-acetic acid and by sodium dodecyl sulfate polyacrylamide gel electrophoresis after disulfide bond-cleavage treatments. Results from these studies suggest the existence of an approximately 67,000-Mr glycoprotein that contains antigenic domains common to proinsulin and insulin.