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Inactivation of 15-lipoxygenases by acetylenic fatty acids
H Kühn1, K Hayess, H G Holzhütter
1Institute of Biochemistry, Medical School (Charité), Humboldt University, Berlin, F.R.G.
Abstract:
The inactivation of soybean lipoxygenase-1 and of rabbit reticulocyte lipoxygenase by five selected acetylenic fatty acids was studied. In all cases the inactivation was time-consuming and depended on the concentration of the inactivator. The inactivation kinetics was measured and the data were fitted to a kinetic model based on the assumption of catalytic self-inactivation. The kinetic constants (Km-value and inactivation rate k2) calculated indicated that 7,10,13-eicosatrienoic acid was the most powerful inactivator for the soybean enzyme followed by 8,11,14-eicosatrienoic acid. The occurrence of an additional triple bond between C-4 and C-5 or between C-5 and C-6 strongly reduced the suicidal rate. With the reticulocyte enzyme, only small differences in the reactivities towards various acetylenic fatty acids have been observed.
Insights
Certain acetylenic fatty acids effectively inactivate soybean lipoxygenase-1, with 7,10,13-eicosatrienoic acid being the most potent. Inactivation of rabbit reticulocyte lipoxygenase showed minimal differences in reactivity among these compounds.
Area of Science:
- Biochemistry
- Enzymology
- Lipid Chemistry
Background:
- Lipoxygenases are key enzymes in lipid metabolism.
- Understanding enzyme inactivation mechanisms is crucial for drug development and biochemical research.
- Acetylenic fatty acids are known to interact with enzyme active sites.
Purpose of the Study:
- To investigate the inactivation of soybean lipoxygenase-1 and rabbit reticulocyte lipoxygenase by selected acetylenic fatty acids.
- To determine the kinetic parameters governing this inactivation process.
- To identify the most effective acetylenic fatty acid inactivators for these enzymes.
Main Methods:
- Enzyme assays were performed to measure the activity of soybean lipoxygenase-1 and rabbit reticulocyte lipoxygenase.
- Inactivation kinetics were studied over time and at varying concentrations of acetylenic fatty acids.
- Data were fitted to a kinetic model assuming catalytic self-inactivation to calculate kinetic constants (Km and k2).
Main Results:
- Inactivation of both enzymes was time-dependent and concentration-dependent.
- 7,10,13-eicosatrienoic acid demonstrated the highest inactivation potency against soybean lipoxygenase-1, followed by 8,11,14-eicosatrienoic acid.
- Additional triple bonds at C-4/C-5 or C-5/C-6 positions significantly reduced the inactivation rate for soybean lipoxygenase.
- Rabbit reticulocyte lipoxygenase exhibited only minor differences in reactivity towards the tested acetylenic fatty acids.
Conclusions:
- Specific acetylenic fatty acids, particularly 7,10,13-eicosatrienoic acid, are potent mechanism-based inactivators of soybean lipoxygenase-1.
- The position of triple bonds in acetylenic fatty acids influences their efficacy as inactivators.
- Rabbit reticulocyte lipoxygenase shows broader substrate specificity or different inactivation mechanisms compared to the soybean enzyme.