Some studies on the relationship between sialic acid and the mucopolysaccharide-protein complexes in human cartilage

Abstract

Crude chondro-mucoprotein preparations, extracted from human cartilage with mild alkali, were fractionated on diethylaminoethylcellulose, with tris-citrate buffers of decreasing pH and increasing ionic strength. Evidence for the presence of sialic acid in the subtractions obtained is reported. Analytical data indicated the presence in cartilage of protein and glycoprotein material unrelated to chondroitin sulphates. About 50% of the crude preparation was not adsorbed on the ion-exchanger. This major subtraction was highly viscous and was probably the fraction responsible for the high viscosity of the chondromucoprotein preparations. The effects of papain, trypsin, hyaluronidase and plasmin on the viscosities of the crude preparations and the major subtraction were investigated. Cleavage of sialic acid in the major subtraction was detected after dissociation of the complex with acid and alkali. The mechanism of release by both reagents appeared different. The cleavage of sialic acid from the various fractions by receptor-destroying-enzyme preparations and crystalline neuraminidase was investigated. The sialic acid in a chondroitin sulphate A-peptide complex was also found to be susceptible to neuraminidase action. Possible relationships between sialic acid and chondromucoprotein are discussed and the hypothesis is advanced that the protein component of the chondromucoprotein molecule is a sialoprotein.