Electron transport in mammalian nuclei II. Oxidative enzymes in a large-scale preparation of bovine liver nuclei

1. A large-scale preparation of highly purified bovine liver nuclei is studied enzymatically. 2. Trace activities of succinate oxidase and NADPH-cytochrome c reductase are ascribed to slight mitochondrial and microsomal contamination, respectively. 3. Rotenone, antimycin A, piericidin A-insensitive NADH-cytochrome c reductase, NADH oxidase, cytochrome c oxidase, glucose-6-phosphatase, and Mg²⁺-stimulated ATPase are shown to be endogenous to nuclei. 4. The O₂ consuming nuclear NADH oxidase differs from its mitochondrial counterpart in its greater resistence to histone inhibition, its susceptibility to inhibition by deoxyribonuclease, its dependency on cytochrome c for activity, and the 10-fold higher concentration of exogenous cytochrome c needed for maximum O₂ consumption. 5. The nuclear cytochrome c oxidase system cannot oxidize tetrachlorohydroquinone in contrast to the mitochondrial cytochrome c oxidase system. 6. The nuclear preparations lack coenzyme Q, a characteristic component of the electron transport system of inner mitochondria membrane. 7. The NADH/cytochrome c oxidase ratio is 1.3 for the nuclear oxidases and 0.59 for mitochondrial oxidases. 8. The NADH oxidases of nuclei, outer mitochondrial membrane and microsomes are discussed.