This technically elegant paper (1) suffers somewhat from the fact that it solely focuses on the glycosaminoglycan chains of the proteoglycans. It is true that the glycan chains are N-acetylated or sulfated in situ while their presentation, e.g. on the cell surface, is greatly determined by the peptide chain they are associated with (2). Most glycosaminoglycan analyses start with proteolysis so that it is understandable that the peptidic portion is overlooked. However, versatile methods exist for the isolation and analysis of proteoglycans as a single entity (2), and they should be applied more widely in glycobiology.
References
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