[Relationship between the apparent order of substrate binding to an enzyme and the nature of the reaction between their active centers].

Studying the kinetics of product formation in multisubstrate reactions catalysed by enzymes with two active sites one can obtain the order of substrate binding opposite to the veritable one. Isotope exchange reaction at chemical greatly differs from the reactions of product formation because cooperative (or anticooperative) interaction of the active enzyme sites does not change the seeming order of substrate binding. The model of two-substrate reaction catalysed by the two-site enzyme where one of the substrate can pass from one active enzyme site to another over the reaction is studied. It is shown that for the present instance the lack of coincidence of true and seemingly mechanisms in isotope exchange reaction may occur. The model is used for the description of isotope exchange reaction catalysed by two-site enzyme aminoacyl-tRNA synthetase. The model is consistent with the experimental data.