Chemical and immunological characterization of proteoglycans of embryonic chick calvaria

Abstract

Proteoglycans of embryonic chick calvarium, a noncartilagenous tissue, were characterized chemically and immunologically. Of the 35SO 2− 4-labeled glycosaminoglycans isolated from 13-day and 17-day-old chick embryos, chondroitin sulfate was the major component (67–88%). Heparan sulfate (5–18%) and keratan sulfate (1–2.6%) were found in smaller amounts. Proteoglycans were labeled with 35SO 2− 4 and isolated by 4.0 M guanidine HCl extraction from calvaria of 13-day-old embryos. The major proteoglycans showed a considerable polydispersity on Sepharose 4B and 6B, and were found to be much smaller (70,000 ± 7,000 daltons) than cartilage proteoglycan subunits and contained only one or two chondroitin sulfate chains with a molecular weight of 41,000 ± 4,000. The results of double immunodiffusion studies and radioimmune inhibition assays using antisera against chick and rat cartilage proteoglycan subunits indicate that chick calvarium contains proteoglycan(s) with at least one species-specific antigenic determinant which cross-reacts with antiserum against chick cartilage proteoglycan subunits. The calvarial proteoglycans showed a significant reactivity toward one of the monoclonal antibodies against chick cartilage proteoglycan subunits, but only a very weak reactivity toward the others as judged by radioimmune inhibition assays.