Immunological studies of bovine nasal cartilage proteoglycan "link proteins".

Bovine nasal cartilage proteoglycan aggregates are dissociated and separated by density gradient centrifugation in 4 M guanidine into proteoglycan subunit (PGS) and glycoprotein link (GPL) fractions, the latter containing hyaluronic acid and "link proteins" responsible for aggregate formation. It was previously concluded on the basis of immunodiffusion studies that GPL has two antigenic components, one in common with PGS and one specific for the link proteins. However, in the present study it was found that antisera to PGS, which should lack link proteins, reacted with both "subunit" and "link" components of GPL, and antisera to fragments of PGS derived from the hyaluronic acid-binding portion of the molecule reacted preferentially with the link component. Reduction and alkylation of GPL led to modification of the reactions of both anti-GPL and anti-PGS sera with its link component. These immunodiffusion results indicate that the proteoglycan subunit and the link proteins are immunologically related and suggest that the link proteins may be identical with and derived from the hyaluronic acid binding portion of the proteoglycan subunit.