Effect of Magnesium Ion on Brain Mitochondrial Respirarion. I. Activation of Brain Mitochondrial Phosphotransferases by Magnesium Ion

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Abstract
The mechanism of respiratory control by ADP in brain mitochondria was analyzed from both respiratory activity and interconversion of adenine nucleotides. The respiration of tightly coupled brain mitochondria was stimulated by added magnesium. The experiments performed under various metabolic conditions indicated that the stimulatory effect of added magnesium ion on state 4 respiration depended on the activation of adenylate kinase [EC 2. 7. 4. 3] and creatine kinase [EC 2. 7. 3. 2], whereas, various other factors participated in the stimulation of state 3 respiration. The influence of hexokinase [EC 2. 7. 1. 1] or ATPase [EC 3. 6. 1. 3] on the stimulation of the state 4 respiration by added magnesium was not observed in the experimental condition studied. These results indicate that, in brain mitochondria, the reactions catalyzed by adenylate kinase and creatine kinase act as a secondary mechanism of respiratory control, and that the reaction catalyzed by creatine kinase competes with the oxidative phosphorylation system for ADP.

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