The binding of cations by chondroitin sulfate.

The polyelectrolyte nature of chondroitin sulfate and related polysaccharides suggests they may bind cations. Since chondroitin sulfate is an extracellular component of mammalian connective tissue, the binding properties of this polyelectrolyte for cations may be of significance in the distribution and storage of extracellular cations. In disease states in which sodium is known to play a major role its storage and distribution may be altered as a result of changes in extracellular polysaccharide metabolism. The purpose of the present study is to determine the binding properties of chondroitin sulfate polyanions for the cations sodium, potassium, and calcium. The results indicate that sodium and potassium are bound to chondroitin sulfate to about the same extent, and that binding of calcium is somewhat greater. Chondroitin sulfate is a salt with a molecular weight of about 20,000 to 30,000 (1), which is often isolated with sodium or potassium as its cation. It is a polymer consisting of about 50 repeating units of the kind represented in Figure 1 (2). If sodium chondroitin sulfate were completely ionized, the resulting polyanion could carry a total negative charge of 100 units per molecule. In the dry neutral salt this charge is balanced by 100 equivalents of cation such as sodium or potassium. Such cations are called counterions. During the past few years, study of several different types of synthetic polyelectrolyte salts has suggested that their ionization in solution is in effect not complete and that part of the total number of counterions may be bound to the polyion (3-9).