Cofactor Requirements for Oxidation of Alpha-Keto Acids by Sweet Potato Mitochondria.

In recent years evidence that suggests the operation of the Krebs cycle in plant tissues has accumulated. Studies by Millerd et al (10), Laties (8), Brummond and Burris (4), Biale and Young (3), and Smillie (14), have demonstrated that mitochondria, isolated by differential centrifugation of tissue homogenates, can carry out oxidation with concomitant phosphorylation of Krebs cycle acids. Davies (5), and Abramsky and Biale (1) have shown by chromatographic techniques that the oxidations of Krebs cycle acids are, in fact, mediated through the Krebs cycle and that pyruvate enters the cycle. However, active mitochondria have been isolated from plants of few species. Most of the tissues used for these studies, except those of Biale and Young (3) and Smillie (14), were either juvenile or etiolated. There is, therefore, a need to extend the knowledge of mitochondrial oxidations to many more plant species and to different tissues. The objective of this study was to isolate and characterize mitochondria from sweet potato roots (Ipomoea batatas Poir.). It was hoped that work with a different species and a different tissue might throw some additional light on mitochondrial activity in plant cells. In most metabolic studies with cytoplasmic particles from plants the rates of pyruvate oxidation were considerably lower than those of the other acids. The cofactors used for activating pyruvate oxidase were virtually the same as those for malate, citrate, etc. The requirement for a primer acid, adenylate, and magnesium was established in the early investigations. It seemed desirable, therefore, to explore more fully the relation of some of the less commonly used cofactors to the oxidation of keto acids. This paper reports the results of such studies.