The metabolic fate of chondroitin (35S)sulphate proteoglycan in the rat.

Revell & Muir (1972) have studied the metabolism of 35S-labelled proteoglycan from porcine cartilage after injection into guinea pigs. They concluded that the polymeric material excreted in the urine was the result of proteolytic degradation of the injected proteoglycan to single chains of chondroitin sulphate. These results are particularly interesting with respect to the site(s) and mechanism(s) of proteoglycan degradation, since it has been shown that single chains of chondroitin 4-[35S]sulphate are taken up by rat liver and degraded with the elimination of inorganic [3sS]sulphate into the blood (Wood et al., 1973). No other 35S-labelled products could be detected. The present investigation was undertaken to determine the nature of labelled polymeric material excreted in the urine of the rat after the administration of 3sS-labelled proteoglycan from cartilage of animals of the same strain. The results show that, in this species, it is not necessary to invoke a proteolytic degradation step to account for the polymeric products in the urine. Rat xiphoid cartilage was labelled with [35S]sulphate as described by Hardingham & Muir (1972) and then extracted with 4 M-guanidinium chloride, yielding asolution from which a preparation corresponding to proteoglycan ‘subunit’ was isolated by preparative ultracentrifugation in a CsCl gradient as described by Hascall & Sajdera (1969). After removal of CsCl and guanidinium chloride by dialysis, the proteoglycan preparation [76 % chondroitin 4-sulphate, estimated as a fraction of total chondroitin sulphate by method I11 of Saito et al. (1968)l was found to have a specific radioactivity of 2.2 pCi/