1. The glycosaminoglycans of human tracheobronchial cartilages from subjects of various ages were liberated by proteolysis of the tissue and purified by ion-exchange chromatography. Purified glycosaminoglycans were fractionated on Dowex 1 resin and cetylpyridinium chloride was used to separate chondroitin sulphates and keratan sulphates occurring in the same fraction. 2. The total chondroitin sulphate content of the cartilages decreased linearly with increasing age. Age-dependent changes in the chemical heterogeneity of chondroitin sulphate were observed, a low-sulphated compound making up 25% of the total glycosaminoglycan at birth but rapidly diminishing in content during the first 6 months of life. Of the total chondroitin sulphate the 6-isomer became rather more prominent than the 4-isomer with increasing age. 3. The total keratan sulphate content of the cartilages increased from trace amounts only at birth to a plateau value by the beginning of the fifth decade. Of the total keratan sulphate approx. 70% was due to a high-molecular-weight compound with a sulphate/hexosamine ratio of 1.5–1.8: 1.0. The degree of sulphation varied between compounds isolated from different individuals. The remaining 30% of the keratan sulphate appeared to be intimately associated with chondroitin 6-sulphate and could only be separated from it after treatment with 0.45m-potassium hydroxide. The hybrid glycosaminoglycans were of lower molecular weight and had a lower sulphate/hexosamine ratio than the major keratan sulphate compound.

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