The Use of Lanthanum to Study the Degradation of a Proteinpolysaccharide from Cartilage.

Chondroitin sulfate occurs in bovine nasal cartilage as compounds with protein called proteinpolysaccharides (PP) of which there are two kinds: (a) the major part is not sedimented at 100,000 X g and is called PP-L; (b) the smaller part is readily sedimented at 10,000 X g and is called PP-H (1). Both, on treatment with NaOH (0.15 in, 25”, 16 hours), yield chondroitin sulfate in amounts corresponding to their galactosamine contents, and keratan sulfate in amounts nearly corresponding to their glucosamine contents (2). Although the chondroitin sulfate is readily separated from the reaction mixture after the breakdown of PI-‘-L is complete, this would not be possible during the early stages of degradation since no method is known, at a preparative level, that would allow quantitative separation of PP-L from chondroitin sulfate. All cationic molecules known to precipitate one also precipitate the other under the same conditions. The present report concerns an unexpected property of the trivalent lanthanum cation that makes possible the separation of mixtures of PP-L and the form of chondroitin sulfate that rep sults from the alkaline breakdown of PP-L. The separation depends on the observation that while PP-L is rather complete13 precipitated from aqueous solution at 5“ by lanthanum, chondroitin sulfate made by alkaline degradation of PP-L is not precipitated at all by addition of lanthanum at 5” but can be precipitated by warming the solution to 50”. These properties of the lanthanum salts have been used to follow the course of the breakdown of PP-L by KOH (0.16 M, 25”) and have shown that it is complete in 120 minutes. This makes it possible to isolate the chondroitin sulfate formed from PP-L by treatment with alkali for a time even less than necessary for its complete liberation, so any degradative changes associated with the much longer treatments commonly used could be studied. The lanthanum fractionation described in the present work coupled with the barium fractionation described earlier (2) makes possible a detailed separation of all the products of degradation of PP-L by alkali at any time from the beginning of this process throughout its course.