In This Paper I shall describe some of the information we have recently obtained regarding the enzymic and molecular organization of the mitochondria, which as you know are very small particulate organelles in the cytoplasm of all aerobic cells. These bodies have been found to catalyze one of the most fundamental activities of the cell, namely, the transformation of the energy yielded by oxidation of foodstuffs into the so-called phosphate-bond energy of adenosine triphosphate. This process of respiration and phosphorylation is extremely complex and involves the interaction of at least seventy different enzymes and coenzymes in an integrated fashion.
The mitochondria have a characteristic ultrastructure in which these enzymes are embedded, and it is now possible to consider in some detail the intramitochondrial location and function of these important energy-transforming molecules.
First, let us consider the organization of oxidative metabolism in purely biochemical terms. Figure 1 shows the usual text-book representation of the final common pathway of biologic oxidation in animal tissues. You will recall that all three of the major foodstuffs of the cell (carbohydrate, fat and protein) ultimately are degraded in the tissues to a two-carbon unit, namely, acetylcoenzyme A. The acetate group then undergoes oxidation by the Krebs citric acid cycle, and in this process the two carbon atoms of acetate become oxidized to carbon dioxide. The oxidation of acetate is finally completed when pairs of hydrogen atoms are removed from certain of the intermediates of the Krebs cycle by dehydrogenases. These hydrogen atoms, or their equivalent in electrons, pass along the respiratory chain via the cytochromes until they meet molecular oxygen and reduce it to form water.
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