Abstract
The activity of UDP-xylose:core protein xylosyltransferase (EC 2.4.2.26) in costal cartilage of young rats (3 months) and old rats (36 months) was measured. The enzyme activity in cartilage of young rats (mean ± S.D.) is 3370 ± 1440 Bq h −1 mg −1 DNA, which is about three times higher than that determined in cartilage of old rats (1090 ± 520 Bq h −1 mg −1 DNA). A similar decrease is found if the enzyme activity is referred to the concentration of extracted protein (young rats 240 ± 90 Bq h −1 mg −1 protein, old rats 70±30 Bq h −1 mg −1 protein). The amount of galactosamine-containing proteoglycosaminoglycans that are extractable with 4 M guanidinium chloride from cartilage is significantly higher in young rats (29.1 ± 4.8 nmol GalN per mg cartilage wet weight) than in old animals (5.8 ± 3.0 nmol GalN per mg cartilage wet weight). Thus, if xylosyltransferase activity is referred to the amount of galactosamine-containing proteoglycans in cartilage, nearly identical values are obtained (young rats, 80 ± 30 Bq h −1 μmol −1 GalN; old rats, 85 ±35 Bq h −1 μmol −1 GalN). The results support the assumption that the synthesis of proteochondroitin sulfate is diminished in costal cartilage of old rats by a mechanism involving a reduced activity of xylosyltransferase.
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