title: The equilibrium assumption is valid for the kinetic treatment of most time-dependent protein-modification reactions.
abstract: To facilitate mechanistic interpretation of the kinetics of time-dependent inhibition of enzymes and of similar protein modification reactions, it is important to know when the equilibrium assumption may be applied to the model: formula: (see text). The conventional criterion of quasi-equilibrium, k + 2 less than k-1, is not always easy to assess, particularly when k + 2 cannot be separately determined. It is demonstrated that the condition k + 2 less than k-1 is necessarily true, however, when the value of the apparent second-order rate constant for the modification reaction is much smaller than the value of k + 1. Since k + 1 is commonly at least 10(7)M-1.S-1 for substrates, it is probable that the equilibrium assumption may be properly applied to most irreversible inhibitions and modification reactions.
mesh_terms: D004791:Enzyme Inhibitors; D007700:Kinetics; D008954:Models, Biological; D011506:Proteins / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D011506:Proteins