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Phosphorylation of mitochondrial membrane proteins: effect of the surface potential on monoamine oxidase
Abstract:
Proteins of mitochondrial membranes become phosphorylated when liver mitochondria are incubated with ATP in the presence of Mg2+. This is accompanied by an increase of the negative surface potential of mitochondrial membranes, as calculated from the dissociation constant of fluorescent probes, 8-anilino-1-naphthalene sulphonate and ethidium bromide, and by a decrease of the apparent Km-value of mitochondrial monoamine oxidase. Protein phosphorylation, the increase of the negative surface potential and the decrease of apparent Km of monoamine oxidase are greatly potentiated by cytoplasmic protein kinases in the presence of cyclic AMP.
Insights
Liver mitochondria proteins get phosphorylated with ATP and Mg2+, increasing negative surface potential and decreasing monoamine oxidase activity. Cytoplasmic protein kinases and cyclic AMP further enhance these effects, impacting mitochondrial function.
Area of Science:
- Mitochondrial biochemistry and cell signaling.
Background:
- Mitochondrial membrane proteins undergo phosphorylation in response to ATP and Mg2+.
- This phosphorylation event influences mitochondrial membrane surface potential and enzyme kinetics.
Purpose of the Study:
- To investigate the effects of protein phosphorylation on mitochondrial membrane properties and enzyme activity.
- To explore the role of cytoplasmic protein kinases and cyclic AMP in modulating these mitochondrial changes.
Main Methods:
- Incubation of liver mitochondria with ATP and Mg2+.
- Measurement of mitochondrial membrane surface potential using fluorescent probes (8-anilino-1-naphthalene sulphonate and ethidium bromide).
- Assay of mitochondrial monoamine oxidase activity to determine apparent Km-values.
Main Results:
- Protein phosphorylation in mitochondrial membranes was observed.
- A significant increase in the negative surface potential of mitochondrial membranes was detected.
- A decrease in the apparent Km-value of mitochondrial monoamine oxidase was measured.
- Cytoplasmic protein kinases and cyclic AMP markedly potentiated protein phosphorylation, increased negative surface potential, and decreased monoamine oxidase Km.
Conclusions:
- Mitochondrial protein phosphorylation alters membrane surface charge and modulates monoamine oxidase activity.
- Cytoplasmic signaling pathways involving protein kinases and cyclic AMP can significantly influence mitochondrial function and biochemistry.