S. O. Karakhim

Palladin Institute of Biochemistry, National Academy of Sciences of Ukraine, Kyiv;
e-mail: laserlab@biochem.kiev.ua

The Slater-Bonner method which is used for graphic determination of substrate constant (K_s) by linear dependence of apparent Michaelis constant (K_m^app) on the limiting rate (V^app) of enzyme-catalysed reactions with activator participation has been critically analysed. It has been shown that although it is possible to record the mechanisms of such reactions as a scheme similar to Michaelis-Menten model which allow to find correlation K_m^app and V^app as equation K_m^app = K_s + V^app/k₁[E]₀ ([E]₀ is a total enzyme concentration, k₁ is a rate constant of enzyme-substrate complex formation from free enzyme and substrate) in order to calculate K_s and individual rate constants (k₁, k_-1), but this approach for investigation of all reactions with activator participation ought not to be used. The above equation is not obeyed in general, it may be true for some mechanisms only or under certain ratios of kinetic parameters of enzyme-catalysed reactions.

S. O. Karakhim

Palladin Institute of Biochemistry, National Academy of Sciences of Ukraine, Kyiv;
e-mail: laserlab@biochem.kiev.ua

The article is dedicated to analysis of equation which expresses apparent Michaelis constant K_m^app of enzyme-catalysed reactions with activator participation by means of the substrate constant K_s and rate constant of enzyme-substrate complex decomposition kcat. It has been shown that although it is possible to record the mechanisms of such reactions as a scheme similar to Michaelis-Menten model and to derive equation of apparent Michaelis constant as K_m^app = K_s + k_cat/k₁, but this approach cannot be used for investigation of all reac­tions with activator participation. The equation mentioned above is not obeyed in the general case, it may be true for some mechanisms only or under certain ratio of kinetic parameters of enzyme-catalysed reactions.