Chondroitin sulfate-protein

The problem of mucopolysaccharide impurities will be discussed at the end of Section VI. This is of great importance to considerations of esterlike linkages as ester links may occur in certain mucopolysaccharides. They have been suggested as the chondroitin sulfate-protein links in a complex isolated from cartilage (Muir, 1958). 

The chondroitin sulfate-protein complex in rat costal cartilage is metabolized as a single unit (G9). Subcutaneous injection of a mixture of DL-lysine-C and Na2S 04 resulted in labeling of both mucopolysaccharide and protein moieties. Since no differences in the rates of turnover of these moieties were apparent, it seems that the entire complex is synthesized as a unit and then extruded into the matrix. The suggestion (G9) that chondroitin sulfate may be released from cartilage in vivo by the action of proteolytic enzymes is not without support (T3). 

C9. Cross, J. I., Mathews, M. B., and Dorfman, A., Sodium chondroitin sulfate-protein complexes of cartilage II. Metabolism. J. Biol, Chem. 235, 2889-2892... 

K30. Kleine, T. O., Heinrich, B., and Goetz, K., Biosynthesis of chondroitin sulfate proteins. Isolation of four pools of chondroitin sulfate proteins differing in their solubility and labeling rates with radiosulfate in calf rib cartilage. FEES (Fed. Euf. Biochem. Soc.) Lett. 31, 170-174 (1973). 

Fio. 4. structure of the carbohydrate sequence of the chondroitin sulfate-protein linkage region (the sulfate group on the galactosamine residue is omitted). 

Although it has long been know n that demiatan sulfate is covalently linked to protein in the tissues, the actual isolation of the protein polysaccharide has only recently been accomplished (Toole and fjowthcr, 1965, 1966, 1968). The dermatan sulfate-protein has a rather high protein content, approximately 50%, and is smaller than most of the chondroitin sulfate-protein complexes, wdth a molecular weight of approximately 100,000-200,000. 

Early studies of the turnover of the chondroitin sulfate protein complex of rat costal cartilage (Gross ei al., I960) show-ed that the carbohydrate and protein moieties were metabolized at the same rate. Similarly, Campo and Dziewiatkowski (1962) found that the formation of both moieties proceeded in a roughly parallel fashion in cartilage preparations incubated in vitro. However, these experiments did not permit any conclusions as to the order in which the tw O components were synthesized. The investigations of the eell-frcc biosynthesis of the protein polysaccharide, reviewed above, have indicated that the synthesis of the protein core, or at least part of it, precedes the formation of the chondroitin sulfate chains and... 

Metabolic Functions. Manganese is essential for normal body stmcture, reproduction, normal functioning of the central nervous system, and activation of numerous enzymes (126). Synthesis of the mucopolysaccharide chondroitin sulfate involves a series of reactions where manganese is required in at least five steps (127). These reactions are responsible for formation of polysaccharides and linkage between the polysaccharide and proteins that form... 

As shown in Figure 48-8, the keratan sulfates consist of repeating Gal-GlcNAc disaccharide units containing sulfate attached to the 6 position of GlcNAc or occasionally of Gal. Type 1 is abundant in cornea, and type II is found along with chondroitin sulfate attached to hyaluronic acid in loose connective tissue. Types I and II have different attachments to protein (Figure 48—8). 

CS-PG, chondroitin sulfate-proteoglycan these are similar to the dermatan sulfate PGs (DS-PGs) of cartilage ffable 48-11). SPARC, secreted protein acidic and rich in cysteine. 

CSPG chondroitin sulfate proteoglycans GAP GTPase-activating protein... 

Core protein -------, chondroitin sulfate + + + + + + +, keratan sulfate xxxxx,... 

The dermis contains several types of cells, including fibroblasts, fat cells, macrophages, histiocytes, mast cells, and cells associated with the blood vessels and nerves of the skin. The predominant cell is the fibroblast, which is associated with biosynthesis of the fibrous proteins and ground substances such as hyaluronic acid, chondroitin sulfates, and mucopolysaccharides. 

Enzymic transfer of D-xylose from uridine 5 -(D-xylopyranosyI-HC pyrophosphate) to L-serine residues of endogenous protein acceptors from (a) a cell tumor of the mouse188 and (b) chick-embryo cartilage189 occurs in cell-free extracts of both of these tissues, in the absence of biosynthesis of protein. The enzyme preparations employed were from the supernatant liquor, although activity was also present in the insoluble fractions. In these two types of tissue, the acceptors are heparin and chondroitin sulfate, respectively, but the presence of other D-xylose-containing glycoproteins in ascites fluid from... 

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