AGGRECAN IN BOVINE TENDON

Large proteoglycans were purified by ion-exchange chromatography, gel filtration and CsCl gradient centrifugation from the compressed and te nsional regions of adult bovine deep flexor tendon. Tryptic peptide ma ps of proteoglycan from the compressed region were very similar to map s of aggrecan from bovine articular cartilage, with evidence for the p resence of all fifteen previously identified markers from the G1, G2 a nd G3 domains. The presence of aggrecan in these samples was confirmed by sequencing the G1 peptide YPIHTPR. The equivalent maps for large p roteoglycan from tensional tendon were also consistent with the presen ce of aggrecan, and this was confirmed by sequencing three marker pept ides from each of the G2 and G3 domains. However, G1 marker peptides w ere conspicuously absent from tensional samples. Northern blots for ag grecan mRNA showed high levels in cells from compressed tendon and art icular cartilage. Extended exposure revealed a lower level of hybridiz ation to RNA from tensional tendon as well. The results confirm that a ggrecan, which is similar in core protein structure to articular carti lage aggrecan, is the predominant chondroitin sulfate-bearing large pr oteoglycan of compressed tendon. The results also indicate that aggrec an fragments lacking the G1 domain can account for the small amounts o f chondroitin sulfate-bearing large proteoglycan in tensional regions of adult tendon.