An oligomycin-resistant Mg2+-dependent ATPase in rabbit bone marrow mitochondria.

Rabbit bone marrow mitochondria isolated by differential centrifugation showed typical oxypolarographic tracings with glutamate oxidation with ADP:O ratio of 2.9. Similar results were obtained with liver mitochondria of the same animal. When marrow mitochondria were oxydizing a substrate such as glutamate, added MgCl2 markedly stimulated state-4 respiration giving a respiratory rate identical to that of state-3. In contrast, no Mg2+-stimulation was observed with liver mitochondria. Oligomycin completely blocked the stimulation by Mg2+ but further addition of 2,4-dinitrophenol reactivated the oxygen consumption by uncoupling. Further purification of marrow mitochondria by density gradient centrifugation in Percoll provided identical oxypolarographic results. Moreover, when marrow mitochondria were incubated without Mg2+, they showed a low ATPase activity that was stimulated by 2,4-dinitrophenol and blocked by oligomycin. The presence of Mg2+ in the incubation medium uncovered an additional ATPase activity which was resistant to oligomycin and apparently unaffected by 2,4-dinitrophenol. It is concluded that bone marrow mitochondria possess two types of ATPase activity distinguished on the basis of their reactivity with oligomycin, 2,4-dinitrophenol and Mg2+.