The Oxidation of Malate by Isolated Turnip (Brassica napusL.) Mitochondria

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Abstract
Washed and purified turnip mitochondria oxidize malate with respiratory control and ADP: O values approaching 3.0 and produce pyruvate as the principal product. Oxaloacetate is also produced in significant amounts but is removed by an endogenous mechanism. Malate dehydrogenase appears to be important to the oxidation of malate but requires the removal of oxaloacetate. During malate oxidation the mitochondria undergo configurational changes similar to those observed in animal mitochondria. Both ‘right side-out’ and ‘inside-out’ submitochondrial particles have been prepared. Right side-out particles oxidize malate in the same way as intact mitochondria, whereas the inside-out particles have a biphasic oxidation, the first phase producing oxaloacetate and the second, NAD-requiring phase producing pyruvate. It is concluded that malate oxidation is a complex process using several enzymes located in the matrix compartment with a minor component possibly on the outer face of the inner membrane.