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Deficiency of uncoupler-stimulated adenosine triphosphatase activity in tightly coupled hepatoma mitochondria
Abstract:
Tightly coupled mitochondria from the well-differentiated hepatoma 7800 failed to exhibit a significant 2,4-dinitrophenol-activated ATPase activity at concentrations of uncoupler sufficient to completely inhibit oxidative phosphorylation. ATPase activity could not be maximally activated by uncoupling agents more potent than 2,4-dinitrophenol, such as carbonylcyanide p-trifluoromethoxyphenylhydrazone and 5-chloro, 3-tert-butyl, 2'-chloro, 4'-nitrosalicylanilide, nor by Mg(++) after the following treatments: sonication, freezing, detergent lysis, and digestion with trypsin. Gel electrophoresis patterns of the membrane proteins of the hepatome mitochondria revealed neither an absence of any one of the three different types of ATPase subunits characteristic of the homogeneous enzyme purified from normal liver mitochondria, nor a deficiency of the oligomeric molecule. Taken together, these data strongly suggest that the supramolecular structure of the membrane ATPase complex of mitochondria from hepatoma 7800 is altered in such a way that its capacity for ATP hydrolysis is severely diminished.
Insights
Mitochondria from hepatoma 7800 show diminished ATP hydrolysis due to altered ATPase complex structure. This impacts cellular energy production in cancer cells.
Area of Science:
- Biochemistry
- Cell Biology
- Oncology
Background:
- Mitochondria are crucial for cellular energy production.
- Hepatoma, a type of liver cancer, often exhibits altered metabolic functions.
- Mitochondrial ATPase is key to ATP synthesis and hydrolysis.
Purpose of the Study:
- To investigate the activity and structure of mitochondrial ATPase in hepatoma 7800 cells.
- To determine if alterations in ATPase function contribute to hepatoma's metabolic changes.
Main Methods:
- Assessing 2,4-dinitrophenol-activated ATPase activity in isolated hepatoma mitochondria.
- Testing activation with potent uncouplers (e.g., CCCP, SNT) and Mg(++).
- Analyzing mitochondrial membrane protein composition using gel electrophoresis.
Main Results:
- Hepatoma 7800 mitochondria showed significantly reduced ATPase activity, even with strong uncouplers.
- Various treatments (sonication, freezing, lysis, trypsin) did not restore maximal ATPase activity.
- Gel electrophoresis confirmed the presence of all ATPase subunits and the oligomeric molecule.
Conclusions:
- The supramolecular structure of the mitochondrial ATPase complex in hepatoma 7800 is altered.
- This structural alteration severely impairs the ATP hydrolysis capacity of the enzyme.
- Dysfunctional mitochondrial ATPase may contribute to the altered energy metabolism observed in hepatoma.