Chondroitin, biosynthesis

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... 

K. Schwarz, B. Breuer, and H.Kresse, Biosynthesis and properties of a further member of the small chondroitin/dermatan sulfate proteoglycan family. J. Biol. Chem., 256 (1990) 22,023-22,028. 

Crocker sarcoma and Mecca lymphosarcoma tumors were found to accumulate the radioselenium slowly and continuously in contrast to rapid uptake and clearance of the label from most normal organs. Clinically, the affinity of tumors for selenium has been the basis for utilizing a radioactive nuclide of selenium as a tumor localizing agent (62, 64) The reason for the localization of selenium is not readily apparent but may reflect enhanced division rates, protein and chondroitin sulfate biosynthesis, or a decrease in the detoxification of selenium. An outgrowth of these observations has been to examine the in vitro effects of selenium supplementation on cellular propagation. 

It comes as no great surprise that trace elements may affect the growth and development of bone. Trace element deficiences profoundly alter hone metabolism in animals either directly or indirectly (3). The absence of a trace element in the diet can lead to inefficient functioning of a specific enzyme or enzymes that require the transition element as a cofactor. An example of this is the role of Cu and iron (Fe) in the cross-linking of collagen and elastins (4-9). The participation of Mn in the biosynthesis of mucopolysaccharides (10-12) is another example. Zn deficiency causes a reduction in osteoblastic activity, collagen and chondroitin sulfate synthesis and alkaline phosphatase activity (13-16). 

Pedersen LC, Tsuchida K, Kitagawa H, Sugahara K, Darden TA, Negishi M. Heparan/chondroitin sulfate biosynthesis. Structure and mechanism of human glucuronyltransferase I. J. Biol. Chem. 2000 275 34580-34585. 

This mucopolysaccharide, possessing a strueture similar to those of chondroitin 4- and 6-sulfates but with a small content of sulfate, was isolated from bovine cornea (M16). Chondroitin resembles hyaluronic acid in its rate of hydrolysis by testicular and bacterial hyaluronidases, but was differentiated from hyaluronic acid ([a]n —65° to — 78°) by its optical rotation ( [o]d — 21°). Its structural similarity to chondroitin 4- and 6-sulfates was indicated by the fact that chondrosine was released in high yield on controlled, acidic hydrolysis (D3). The isolation of this mucopolysaccharide is of particular interest since it may be a precursor in the biosynthesis of chondroitin 4- and 6-sulfates. 

The initial stages of chondroitin and heparan sulfate biosynthesis. Each enzyme is defined by its shorthand name(s) as well as by the abbreviations of the relevant known or proposed corresponding Drosophila and Caenorhabditis genes... 

Hyaluronan p-GlcA/ -(1 3)-p-GlcNAc/ -(l ). The biosynthesis proceeds, apparently without any primer requirement (unlike heparan and chondroitin), by stepwise addition of UDPGlcA and UDPGlcNAc, from the non-reducing end. As with heparan, the synthetases are single polypeptides which catalyse both transfer reactions. 

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