Artificial Allosteric System 5. Allosteric Gain, Total Cooperativity and Local Cooperativity as Appropriate Indices for Allosteric Effect

Abstract Magnitude of cooperativity of a hypothetical m‐subunit allosteric system of hemoglobin type is discussed, based on computation of the amount of O2 to be transferred to the corresponding monomeric nonallosteric system of myoglobin type. For quantitative discussion, “allosteric gain” is defined as the difference between the amount of O2 to be transferred from the allosteric to the nonallosteric system and that from the hypothetical system of average O2 affinity to the nonallosteric system. These two quantities, allosteric gain and amount of O2 transfer, are quite sensitive to equilibrium constant ratio, especially Km/K1, (Ki+1/Ki)max, and i. Hill's coefficient appropriately describes neither the amount of O2 transferred nor allosteric gain. Allosteric gain or the amount of O2 transfer which is best characterized by the total cooperativity index (Km/K1) and the local cooperativity indices (Ki+1/Ki) seem to be appropriate measures of the magnitude of cooperativity.