Abstract
1. 1. Low concentrations of Mg 2+ stimulate both the ATP-ase activity and oxidative phosphorylation of the mitochondrial sub-unit obtained by treatment of liver mitochondria with digitonin. The stimulation of oxidative phosphorylation is not due to an activation of the hexokinase used to trap the ATP-ase but is due to a requirement for Mg 2+ in oxidative phosphorylation. 2. 2. Concentrations of Mg 2+ above 0.0005 M inhibit the ATP-ase and above 0.001 M inhibit oxidative phosphorylation. The inhibition of oxidative phosphorylation is probably caused by the stimulation by Mg 2+ of the hydrolysis of an intermediate in the oxidative phosphorylation reaction. 3. 3. It is concluded that the Mg 2+-stimulated ATP-ase and the DNP-stimulated ATP-ase differ in the nature of their hydrolytic reaction, but that both contain the same phosphorylation reaction, which is moreover the same as that in oxidative phosphorylation, but in the opposite direction.
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