Characteristics of External NADH Oxidation by Beetroot Mitochondria

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Abstract
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. 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. These mitochondria probably possess a rapid oxaloacetate-transporting system.