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Articles

Characteristics of External NADH Oxidation by Beetroot Mitochondria ¹

^a Department of Botany, University of Adelaide, Adelaide, S.A. 5001, Australia

Mitochondria isolated from fresh red beetroot (Beta vulgaris L.) tissue do not oxidize external NADH with O₂ as the electron acceptor. These mitochondria have a rotenone- and antimycin-insensitive pathway of NADH oxidation associated with the outer membrane and are capable of reducing cytochrome c or potassium ferricyanide. They are also capable of oxidizing internal NADH via the inner membrane electron transport chain with normal rotenone and antimycin sensitivity and ADP/O ratios. They differ from other plant mitochondria in the apparent lack of the NADH dehydrogenase located on the outer surface of the inner membrane. It is shown that this activity develops during the aging of red beetroot slices in aerated dilute CaSO₄ solutions, and is present in the mitochondria isolated from aged tissue.

Mitochondria isolated from fresh red beetroot tissue are capable of oxidizing external NADH via a malate-oxaloacetate shuttle system. It is suggested that these mitochondria possess a rapid oxaloacetate-transporting system.

Present address: Department of Botany, University of Illinois, Urbana, Ill. 61801.

³ Supported by the Tertiary Education Assistance Scheme.

¹ This study was supported by the Australian Research Grants Committee.