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[Deamination of nitrogenous compounds in mitochondrial membranes under stimulation of lipid peroxidation]
Abstract:
Fragments of mitochondrial membranes, obtained by freezing-thawing of mitochondrial fraction from rat liver homogenate, were treated with Fe2+ ions under conditions, which were optimal for accumulation of a product of lipid peroxidation--malondialdehyde (MDA). The accumulation of MDA in the mitochondrial membranes was accompanied by a decrease in deamination of monoamines (tyramine or, especially, tryptamine) and by appearance of qualitatively new properties to deaminate histamine or cadaverine as well as adenylic acid. Appearance of these properties was prevented by blocking with trans-2-phenylcyclopropylamine or N-methyl-N-benzylpropynylamine of the mitochondrial monoamine oxidase activity. Inhibitors of initiated by free radicals lipid peroxidation (propylgallate, butyl hydroxytoluene) did not bind Fe2+ ions but prevented the alterations in deamination of nitrogenous compounds induced by the treatment of the fragments of mitochondrial membranes with Fe2+ ions. Stimulation of lipid peroxidation in mitochondrial membranes was, thus, accompanied not only by partial inactivation of the structure-bound monoamine oxidase but also by apparent qualitative alteration (transformation) in its catalytic properties.
Insights
Iron (Fe2+) treatment of rat liver mitochondrial membranes initiated lipid peroxidation, altering monoamine oxidase activity. This process changed the enzyme's substrate specificity and catalytic properties, impacting nitrogenous compound deamination.
Area of Science:
- Biochemistry
- Mitochondrial Biology
- Enzymology
Context:
- Mitochondrial membranes are crucial for cellular respiration and contain enzymes like monoamine oxidase (MAO).
- Lipid peroxidation, a process involving free radicals, can damage cellular structures, including mitochondria.
- Iron ions (Fe2+) are known to promote lipid peroxidation.
Purpose:
- To investigate the effects of Fe2+-induced lipid peroxidation on the catalytic properties of mitochondrial monoamine oxidase.
- To determine if lipid peroxidation alters the substrate specificity and activity of MAO in rat liver mitochondria.
Summary:
- Treatment of rat liver mitochondrial membranes with Fe2+ ions induced lipid peroxidation, evidenced by malondialdehyde (MDA) accumulation.
- This peroxidation led to decreased deamination of tyramine and tryptamine, but induced new deamination capabilities for histamine and cadaverine.
- Specific MAO inhibitors prevented these alterations, while lipid peroxidation inhibitors blocked the changes in deamination properties, indicating MAO involvement.
Impact:
- Fe2+-induced lipid peroxidation not only partially inactivates mitochondrial MAO but also significantly alters its substrate specificity and catalytic function.
- These findings highlight a novel mechanism by which oxidative stress can modify enzyme activity within mitochondria.
- Understanding these alterations is crucial for comprehending mitochondrial dysfunction in various pathological conditions associated with oxidative stress.