Age-related changes in the incorporation of [35S]sulfate into two proteoglycan populations from human cartilage

From human hyaline cartilage (processus xyphoid) preincubated in the presence of [35S]sulfate, proteoglycans were extracted by 4M guanidinium chloride and divided into 6 age groups. Fractionation of proteoglycans by gel filtration under dissociative conditions resulted in two proteoglycan fractions (a and b) with different hydrodynamic volumes. The higher molecular weight fraction a contained chondroitin sulfate, the fraction b keratan sulfate as predominant glycosaminoglycan, the chondroitin sulfate/keratan sulfate ratio decreasing with increasing age in either fraction. The relative portion of proteoglycan fraction b and its 35S-labelling increased with increasing age. From the specific 35S radioactivities of the chondroitin sulfate and keratan sulfate preparations, the occurrence of two independent proteoglycan populations is suggested. A precursor-product relationship between proteoglycan fraction a and b could be excluded.