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How did studies of isolated mitochondria reveal their role in the tricarboxylic acid cycle?

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Diagram illustrating metabolism with two sections: anabolic reaction on the left shows energy used to build larger molecules from smaller ones, while catabolic reaction on the right shows larger molecules breaking down into smaller molecules with energy released. — Metabolomics In anabolic reactions, a cell uses energy to combine small molecules into larger molecules. In catabolic reactions, molecules are broken down, and energy is released.

Studies of isolated mitochondria were instrumental in confirming their role as the site of the tricarboxylic acid (TCA) cycle. Researchers utilized techniques such as tissue homogenization to disrupt cells and remove debris, allowing them to isolate specific organelles through careful centrifugation at increasing speeds.1

By obtaining fractions containing predominantly mitochondria, scientists were able to test these organelles for their capacity to carry out specific metabolic steps. These experiments demonstrated that isolated mitochondria catalyze the oxidation reactions of the TCA cycle and also house the enzymes required for fatty acid oxidation. This approach allowed biochemists to move beyond studies of whole organisms or tissues, which could not reveal the detailed enzymatic steps of metabolic pathways, and instead observe the cycle's function in a controlled, cell-free environment. These findings confirmed that the mitochondrial matrix contains the enzymes necessary to metabolize nutrients into by-products for energy production.12