Lysosomal Degradation of Heparin and Heparan Sulphate
This review is a limited update of a previous review of enzymes that degrade heparan sulphate (HS) and heparin (Hopwood, 1989). Newly-synthesised HS proteoglycan (HSPG) is internalised from the cell surface and catabolised with a half-time of 4 to 6 h in rat ovarian granulosa cells (Yanagishita and Hascall, 1984), and by more than 28 h in human colon carcinoma cells (Iozzo, 1987). Studies of both cell types have shown the existence of preliminary protease and an initial endoglycosidase activity in non-lysosomal (chloroquine-insensitive compartments) to generate HS intermediates of Mr 10 kDa, and further chloroquine-sensitive endoglycosidic activity to produce HS fragments of Mr 5 kDa which are rapidly degraded in the lysosome by a series of exohydrolases to monosaccharides and sulphate without the generation of intermediates. A number of distinct lysosomal membrane transporters are involved in the efflux of the monomeric products GlcNAc, GlcA and IdoA and sulphate ions from the lysosome (Jonas et al., 1989; Jonas and Jobe, 1990a, 1990b; Mancini et al., 1989) which can be reutilised in biosynthetic pathways (Rome and Hill, 1986).
KeywordsPolypeptide Oligosaccharide Monosaccharide Chloroquine Disaccharide
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