Depolymerisation and desulphation of chondroitin sulphate by enzymes from embryonic chick cartilage

Abstract

Previous studies on the degradation of the chon- droitin sulphate proteoglycan in cartilage have indi- cated that the process is initiated extracellularly by limited proteolytic cleavage of the molecule [ 11. Partially degraded proteoglycan may subsequently become incorporated into the chondrocytes for fur- ther, intracellular, breakdown [2,3]. However, lit- tle is known about the enzymes involved in the in- tracellular degradation of chondroitin sulphate in cartilage. Indirect evidence for the occurrence of chondrosulphatase(s) has been obtained in experi- ments with embryonic chick cartilage [2]and with rat costal cartilage [3], respectively, in organ culture. Attempts to demonstrate the presence of an endo- polysaccharidase, acting on the chondroitin sulpha- te chain, have been unsuccessful [4]. The present investigation was undertaken in or- der to establish more conclusively the occurrence in the chondrocyte of chondroitin sulphate-degra- ding enzymes. The results demonstrate the presence of an endopolysaccharidase and a sulphatase, in a lysosomal fraction from this cell. The activity of each enzyme was tested and verified by use of radio- actively labelled chondroitin sulphate, and/or oligo- saccharides thereof, as substrates. 2.