[LIPOXYGENASES AND PLANT CELL METABOLISM REGULATION].

Lipoxygenases are widespread plant enzymes that catalyze the peroxidation of polyunsaturated fatty acids. This reaction is pivotal in the enzymatic cascade that leads to production of numerous metabolism regulators named oxylipins. The activity of these biologically active substances is directly associated with defence reactions in conditions of biotic and abiotic stresses as well as with the regulation of plant growth, propagation and senescence.

[Inhibiting properties of stable nitroxyl radicals in reactions of linoleic acid and linoleyl alcohol oxidation catalyzed by 5-lipoxygenase].

The inhibiting effects of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and its 4-substituted derivatives in reactions of linoleyl acid or linoleyl alcohol oxidation catalyzed by potato tuber 5-lipoxygenase were investigated. Inhibiting properties of stable nitroxyl radicals in presence of lubrol and SDS were reduced at the transition from TEMPO to 4-hydroxy-TEMPO or 4-amino-TEMPO and increased at use of adamantane-1-carboxylic or 3-methyladamantane-1-carboxylic acid 1-oxyl-2,2,6,6-tetramethylpiperidine-4-yl esters. Enzyme activity at saturating concentrations of inhibitor was not suppressed completely, and decreased up to the certain level determined by the substrate nature.

[Hydrophobic nitroxyl radicals inhibit linoleyl alcohol oxidation by 5-lipoxygenase].

The linoleyl alcohol oxidation catalyzed by potato tuber 5-lipoxygenase was found to be efficiently inhibited by stable nitroxyl radicals: 1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl 1-bicyclo[2,2,2]octane-1-carboxylate, 1-adamantylacetate, dodecanoate, and octadecanoate. The dependence of apparent IC50 values on the rotational correlation times of times of 4-hydroxy-1-oxyl-2,2,6,6-tetramethylpiperidine and its derivatives in model micellar systems was analyzed. The inhibition mechanism was proposed; it involves the interaction of hydrophobic nitroxyl radical with the intermediate radical enzyme-substrate complex.