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 O 2 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 O 2 to be transferred from the allosteric to the nonallosteric system and that from the hypothetical system of average O 2 affinity to the nonallosteric system. These two quantities, allosteric gain and amount of O 2 transfer, are quite sensitive to equilibrium constant ratio, especially K m /K 1 , ( K i+1 / K i ) max , and i. Hill's coefficient appropriately describes neither the amount of O 2 transferred nor allosteric gain. Allosteric gain or the amount of O 2 transfer which is best characterized by the total cooperativity index ( K m /K 1 ) and the local cooperativity indices ( K i+1 /K i ) seem to be appropriate measures of the magnitude of cooperativity.