Fig. 5.

Models for thermodynamic linkage of PKR dimerization and heparin binding. (a) Linked model. (b) Unlinked model. P, PKR; H, heparin. The binding constants are defined as follows: L₂₀ is the dimerization constant for unliganded PKR, L₂₂ is the dimerization constant for the PH complex, L₂₁ is the dimerization constant for the interaction of P and PH, β₁₁ is the constant for heparin binding to the PKR monomer, β₂₁ is the constant for heparin binding to the PKR dimer, and β₂₂ is the overall constant for the interaction of two heparin monomers with the PKR dimer to produce P₂H₂. The nomenclature was adapted from Fig. 6-5 in Wyman and Gill.⁴⁰