Some studies on the control of respiration in rat brain mitochondrial preparations

Brain mitochondria have been prepared by a modification of the method described by Tanaka and Abood (5c). This preparation has been shown by electron microscopy to be free of other subcellular components. The ability of low concentrations of Mg 2+ ions to decrease the state 4 rate of respiration and thus increase the respiratory control ratios has been shown. A comparison is made with brain mitochondria prepared in other laboratories, in regard to the effect of Mg 2+ ions on respiration since others have shown variable effects of Mg 2+ ions on respiration. Our preparations demonstrated very high respiratory ratios at μ m concentrations of MgCl 2, the change being mainly in the decreased state 4 rate. The Crabtree-like effect observed in ascites tumor mitochondria has been observed in our brain mitochondrial preparations, and the role of mitochondrially bound hexokinase is discussed with respect to the possible physiologic significance of its localization in isolated brain mitochondria.