The nature of the link between protein and carbohydrate of a chondroitin sulphate complex from hyaline cartilage

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Abstract
A chondroitin sulfate complex was extracted from pig tracheal cartilage with CaCl2. After purifying there remained nearly 10% of protein. Contamination by other polysaccharides was excluded. The complex was electrophoretically homogeneous and did not dissociate at high ionic strengths. Its high viscosity depended upon the integrity of the protein component, which was destroyed by papain but which was resistant to trypsin and chymotrypsin, and partially resistant to pepsin. Dilute alkali also brought about a large fall in viscosity, after which chondroitin sulfate entirely free of amino acids was obtained from the crude material by the same procedure as had been used to purify the complex. Quantitative amino acid analysis showed that the complex contained considerably more dicarboxylic than basic amino acids and a large amount of serine. After digestion with papain half the original amount of serine was left, whereas the quantities of the other amino acids which remained were very much less. A small proportion of the total hexosamine and inorganic sulfate appeared in ultrafiltrates. Ultrafiltrates obtained from the purified complex and from that which had been isolated again after digestion with papain contained no hexosamine sulfate or amino acids, until treated with dilute alkali, when amino acids appeared in the same relative proportions as were present in the original materials, together with some sulfate and hexosamine. It is concluded that the complex consists of polysaccharide chains of variable but moderate length, cemented together by polypeptide units attached to carbohydrate by a bond as sensitive to alkali as an ester or lactone.