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Protein phosphorylation in plant mitochondria.
1Department of Agricultural Biochemistry, University of Nebraska, Lincoln, Nebraska 68583-0718.
Plant Physiology
|September 1, 1985
Summary
Plant mitochondria possess protein kinase activity, phosphorylating endogenous and exogenous proteins. This activity, observed across multiple plant species, suggests similarities with animal mitochondrial protein phosphorylation.
Area of Science:
- Biochemistry
- Plant Biology
- Cell Biology
Background:
- Mitochondria play crucial roles in cellular energy production and signaling.
- Protein phosphorylation is a key regulatory mechanism in eukaryotic cells.
- Understanding plant mitochondrial protein phosphorylation is essential for deciphering cellular processes.
Purpose of the Study:
- To investigate the presence and characteristics of protein kinase activity in plant mitochondria.
- To identify the substrates and regulatory properties of plant mitochondrial kinases.
- To compare plant mitochondrial protein phosphorylation with that of animal mitochondria.
Main Methods:
- Isolation of osmotically lysed mitochondria from various plant species (corn, pea, soybean, wheat, potato).
- In vitro kinase assays using adenosine triphosphate (ATP) and magnesium ions (Mg2+) to phosphorylate endogenous and exogenous proteins.
- Denaturing electrophoresis to analyze the molecular weight of phosphorylated polypeptides.
- Enzyme kinetic studies to determine optimal pH, ATP K(m), and the effect of various inhibitors.
Main Results:
- Protein kinase activity was detected in mitochondria from all tested plant species.
- Eight to fifteen endogenous mitochondrial polypeptides were phosphorylated, with a major 47,000 molecular weight polypeptide identified across species.
- Phosphorylation kinetics showed a biphasic pattern, rapid initially and slower thereafter.
- Optimal kinase activity occurred at neutral to alkaline pH, with an ATP K(m) of approximately 200 micromolar.
- The kinase was inhibited by calcium chloride (CaCl2) but unaffected by sodium fluoride (NaF), calmodulin, oligomycin, or cyclic adenosine monophosphate (cAMP).
Conclusions:
- Plant mitochondria exhibit significant protein kinase activity.
- The identified major phosphorylated polypeptide and kinase properties suggest conserved mechanisms.
- These findings indicate potential similarities between plant and animal mitochondrial protein phosphorylation pathways.