On the relationship between the hill coefficients for steady-state and transient kinetic data: A criterion for concerted transitions in allosteric proteins

A frequently used measure for the extent of cooperativity in ligand binding by allosteric proteins is the Hill coefficient. Hill coefficients can be m easured for steady-state kinetic data and also for transient kinetic data. Here, the relationship between the two types of Hill coefficients is analys ed. It is shown that a value of 1 for the ratio of the two Hill coefficient s is a test for a concerted ligand-induced transition between two conformat ions of the protein, in accordance with the Monod-Wyman-Changeux model. A v alue of 1 for this ratio has recently been observed for a series of chapero nin GroEL mutants suggesting that ATP-induced allosteric transitions in thi s protein ale concerted. (C) 2000 Society for Mathematical Biology.