[Thermoinactivation of potato 5-lipoxygenase and effect of phosphatidic acid on activation energy of denaturation].

The investigation aim was to establish the structural-functional relations of individual lipid metabolism components: enzymes--lipoxygenases and membrane phospholipids. Influence of phosphatidic acid (PA)--allosteric activator of potato tuber 5-lipoxygenase (5-LO)--on thermoinactivation thermodynamic parameters of enzyme was studied. It was established that PA changes essentially the 5-LO thermostability, namely activation energy Ea of enzyme denaturation increases several times in this phospholipid presence. Such changes can evidence that PA interaction with 5-LO leads to conformational changes of enzyme probably due to hydrophobic interactions. Obtained results give a possibility to interpret the action mechanism of PA as 5-LO allosteric activator, which can displace the substrate molecules in binding sites and increase the level of formation of specific products of linoleic acid oxygenation by 5-LO.

[Interaction between 5-lipoxygenase and allosteric effector--sodium dodecyl sulfate].

The role of allosteric effector--sodium dodecyl sulfate (SDS) in the lipoxygenase catalysis in micelle system has been studied. The effect of the stable hydrophobic bis-nitroxides, blocking the free radical transformation, on the oxidation of linoleic acid or linoleic alcohol by 5-lipoxygenase from potato tuber has been investigated. The inhibiting effect of nitroxide compounds on oxidation of linoleic acid or linoleic alcohol by 5-lipoxygenase depends on SDS concentration. The inhibition percentage is determined by the substrate nature and presence of allosteric effector. The presence of SDS did not lead to an appreciable change in the pKa values of ionogenic enzyme groups. The effect of SDS and micellar system on thermodynamic parameters for thermoinactivation of 5-lipoxygenase was studied. It was found that thermoinactivation rate constants and activation energy of enzyme thermoinactivation were increased in the presence of SDS. It is suggested that interaction of 5-lipoxygenase and allosteric effector--SDS intensifies the dissociation of radical intermediates from the active site of the enzyme. These findings are of physiological significance in the light of the lipoxygenase involvement in the membrane lipid peroxidation.