Tag Archives: catalysis

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.

Lipoxygenases and their metabolites in formation of plant stress tolerance

L. M. Babenko1, M. M. Shcherbatiuk1, T. D. Skaterna2, I. V. Kosakivska1

1M.G. Kholodny Institute of Botany, National Academy of Sciences of Ukraine, Kyiv;
2Palladin Institute of Biochemistry, National Academy of Sciences of Ukraine, Kyiv;
e-mail: lilia.babenko@gmail.com

The review focuses on the analysis of new information concerning molecular enzymology of lipoxygenases – proteins involved in lipid peroxidation and found in animals and plants. Modern concept of structural features, catalytic characteristics and functions of lipoxygenase family enzymes as well as products of their catalytic activity in plants have been discussed and summarized. Issues of enzyme localization in plant cells and tissues, evolution and distribution of lipoxygenases, involvement in production of signaling substances involved in formation of adaptation response to abiotic and biotic stress factors and in regulation of lipoxygenase signal system activity are highlighted. Participants of the elements signaling of LOX-pathway reception and transduction into genome are considered. Special attention is given to jasmonates, metabolites of the allene oxide synthase branch of the lipoxygenase cascade, because these metabolites have high biological activity, are ubiquitously present in all plant organisms, and are involved in regulation of vitally important processes. Data concerning lipoxygenase phylogeny, possible occurrence of a common predecessor for modern isoforms of the enzyme in pro- and eukaryote have been examined. Some results of our studies that open up possibilities of using the lipoxygenase catalytic activity characteristics as biological markers in plant stress tolerance researches are given.