Quantitation of Proteoglycans in Biological Fluids Using Alcian Blue

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Abstract

Alcian blue is a tetravalent cation with a hydrophobic core that contains a copper atom, hence its blue color (1). The four charges allow Alcian Blue to bind to gly-cosaminoglycans (GAGs) at high ionic strength, in contrast to other cationic dyes, which are all monovalent. The molecular structure, that is, the plane tetragonal hydro-phobic core with positive charges attached at its corners, may facilitate formation of aggregates of several molecules side by side rather than micelle formation. The ionic strength and presence of other detergents will affect the size of these aggregates in solution. Such positively charged linear aggregates will bind strongly to some negatively charged polymers such as GAGs, but not to others such as nucleic acids reflecting the conformation of both the polymer and the dye. Alcian blue is not a well defined substance. There are large differences in solubility and binding characteristics among different manufacturers but also between batches from the same manufacturer. In addition, the stain has a limited shelf life and is slowly degraded both in solution and as dry substance.