Electron transport systems in the membranes of rat liver nuclei and microsomes and of hepatoma 22a

: It was shown that in contrast to normal liver cells the electron transport in the nuclear membranes of ascite hepatoma 22a cells proceeds much faster than that in microsomes. Using superoxide dismutase-sensitive adrenaline oxidation as an index of O2 formation, it was found that the hepatoma nuclear membranes contain an active O2-producing enzymatic system of a new type. This system differs from those described previously, e.g. it utilizes not only NADPH but also NADH as electron donors and reveals a high sensitivity to cyanide ([I] 50% approximately 10 mkM) and azide ([1] 50% approximately 0.2 mM). It is assumed that the site of cyanide-sensitive generation of O2 radicals in hepatoma 22a nuclei is the cytochrome fraction of the b5 type; the latter is activated by terminal desaturase of fatty acids. The high activity of O2 formation in ascite hepatoma nuclei associated with a low superoxide dismutase activity typical for the tumours suggests a shift in the equilibrium between generation and dismutation of O2 radicals in ascite hepatoma cells. The role of this shift in the selective action of some anticarcinogenic antibiotics, whose effects are mediated by O2 radicals, is discussed.