The oxidation of cytosolic NAD(P)H by external NAD(P)H dehydrogenases in the respiratory chain of plant mitochondria

The respiratory chain of plant mitochondria differs from that in mammalian mitochondria by containing several rotenone‐insensitive NAD(P)H dehydrogenases. Two of these are located on the outer, cytosolic surface of the inner membrane. One is specific for NADH, the other for NADPH. Only the latter is inhibited by diphenyleneiodonium (DPI). Both of these enzymes are normally dependent upon Ca2+ for activity and this constitutes a potentially important mechanism by which the cell can regulate the oxidation of cytosolic NAD(P)H via the concentration of free Ca2+. This and other potential regulatory mechanisms such as the substrate concentration and polyamines are discussed.