Thermodynamics of mucopolysaccharide–dye binding. II. Binding constant and cooperativity parameters of acridine orange–dermatan sulfate system

In the acridine orange–dermatan sulfate system, free and bound dye can be distinguished from each other spectroscopically. This permits the use of fluorometric methods to study the binding of acridine orange to the acid mucopolysaccharide dermatan sulfate. Experiments were conducted at 24°C in 10−3 M citrate/phosphate buffer at pH = 7.0. The binding of the dye is highly cooperative, as evidenced by considerable interaction between adjacent bound dye molecules. Analysis of the data indicates that dermatan sulfate binds 2.3 ± 0.3 mol of acridine orange per dermatan sulfate uronic acid residue with a cooperative binding constant, Kq ranging from 4.9 to 6.0 × 105 M−1 which corresponds to a free energy of 7.74 ⩽ ΔG° ⩽ 7.86. The cooperativity parameter q apparently increases with increasing polymer‐to‐dye ratio.