Physical and immunochemical properties of low-buoyant-density proteoglycans from avian cartilage

Abstract

A proteoglycan link fraction (A 1D 5) from avian xyphoid cartilage contains one link protein and low-buoyant-density proteoglycans. An antiserum made against this fraction (anti-A 1D 5 serum) specifically binds [ 35S]sulfate-labeled proteoglycans from aggregate (A 1), monomer (A 1D 1), and link (A 1D 5) fractions synthesized by 14-day embryonic chick sterna. When [ 35S]sulfate-labeled proteoglycans from either monomer (A 1D 1) or link (A 1D 5) fractions are used as the antigen, anti-A 1D 5 serum binds as well as an antiserum against a purified monomer preparation (anti-A 1D 11400 Vo serum). However, reduction and alkylation of the proteoglycans from the monomer fraction does reveal differences in the binding of the two antisera. Whereas reduction and alkylation of the antigen ( 35S-A 1D 1) inhibit binding by both antisera, binding of the anti-A 1D 5 serum is more affected by antigen alteration. Differences in the two antisera can also be detected in assays using labeled aggregate as antigen. Anti-A 1D 5 serum cannot maintain the same levels of antigen binding as the anti-A 1D 1-1400 Vo serum when compared in an antibody dilution curve. In addition, anti-A 1D 1-1400 Vo serum can stabilize aggregate during sedimentation in a sucrose density gradient containing 4 m guanidine hydrochloride whereas anti-A 1D 5 serum cannot. These results suggest that the low-buoyant-density proteoglycans found in the link (A 1D 5) fraction from avian cartilage contain some of the antigenic determinants found on the proteoglycan monomer. However, there is at least one monomer determinant which is not present in the A 1D 5 fraction.