English: Biochemical showing the characteristically sigmoidal curves generated by using the Hill equation to model coperative binding in biochemistry. Each curve represents a different Hill coefficient: light blue corresponds to n=0.5, red to n=1, gray to n=2, yellow to n=3, and dark blue to n=4. The vertical axis displays the Fraction (Theta) of occupied ligand-binding sites on a protein receptor, equal to ratio of the concentration of Ligand-bound Protein ([PLn_Total]) to the total concentration of Protein receptor ([P_Total]). The horizontal axis is the ratio of the ligand concentration producing half occupation (K_A) to the total Ligand concentration ([L]).