Tag Archives: rate constant
Consideration of the contribution of chemical (non-enzymatic) conversion of substrate in the general mechanism of enzyme reaction
S. O. Kosterin, S. O. Karakhim, P. F. Zhuk
Palladin Institute of Biochemistry, National Academy of Sciences of Ukraine, Kyiv;
e-mail: kinet@biochem.kiev.ua; laserlab@biochem.kiev.ua
Received: 13 September 2018; Accepted: 13 December 2018
When enzyme-catalyzed reactions are studied, it is necessary to take into account the contribution of the chemical (non-enzymatic) conversion of the substrate to the product, which is carried out together with the enzyme-catalyzed conversion of the substrate. It is generally believed that the difference of the product concentration that was formed in the presence of the enzyme and in its absence (during the same time interval) is the concentration of the product that was formed directly in the enzyme-catalyzed reaction, i.e. that there is additivity of the product concentrations at each time point. In this paper, we have analyzed when there is additivity and how to correctly take into account the contribution of chemical (non-catalytic) substrate conversion when the enzyme-catalyzed reactions are investigated. We have shown that the additivity of product concentrations and initial rates is observed only for a period when the product concentration increases linearly with time. The longer the reaction proceeds the more the deviation from the additivity. Under equilibrium condition, there is no additivity of equilibrium product concentrations but under conditions of detailed balance the equilibrium product concentration of the overall reaction, including the enzyme-catalyzed and chemical (non-enzymatic) conversion of the substrate, is also at the same time the equilibrium concentration of the product of the enzyme-catalyzed conversion of the substrate.
Kinetic parameters of polyreactive immunoglobulins interaction with antigens in the presence of protamine
S. A. Bobrovnik, M. O. Demchenko, S. V. Komisarenko
Palladin Institute of Biochemistry, National Academy of Sciences of Ukraine, Kyiv;
e-mail: s-bobrov@bk.ru
The discovered earlier phenomenon of the enhancment of polyreactive immunoglobulines (PRIGs) binding to antigens in the presence of protamine and Tween 20 was investigated in more details. The comparative analysis of PRIGs reaction dynamics with immobilized antigen was provided. In addition, the rate constants for the reaction and the affinity constants of PRIGs-antigen binding in the presence or absence of optimal protamine concentration were determined. The rate constant of PRIGs-antigen reaction did not increase in the presence of protamine optimal concentration and was even reduced approximately twice. However, in the presence of protamine the concentration of reactive PRIGs molecules, that were able to interact with antigen, increased approximately 30 times, and this led to strong reaction rate increase. Protamine also influenced the affinity constant of PRIGs-antigen binding, which increased approximately three times. The suggestion was made that such protamine effect was due to its influence on the PRIGs molecules special structure, and, as a result of the conformational change PRIGs became able to bind more effectively to the antigens.