Organelle-specific NADPH thioredoxin reductase in plant mitochondria

Plant mitochondria contain one or two specific mt-thioredoxins which partic ipate, inter alia, in the regulation of the ketoglutarate dehydrogenase com plex. The presence of thioredoxin reductase, second component of a typical thioredoxin system inside mitochondria has, however, remained uncertain. We here show that potato tuber mitochondrial lysates contain an enzyme of 40 kDa monomer mass, utilizing NADPH and plant (but not bacterial) thioredoxin s as substrates, It is distinct From a 35 kDa reductase of cytosolic origin . Plants thus contain a third thioredoxin reductase, mt-NTR, in addition to the known NTR and ferredoxin-dependent FTR enzyme.