This paper by R. J. Pennington investigates the biochemical abnormalities associated with primary myopathies, particularly focusing on the mitochondrial succinate dehydrogenase and adenosine triphosphatase (ATPase) activities in dystrophic mouse muscle. The study uses a strain of mice with an autosomal recessive gene causing a muscular dystrophy, which has facilitated the exploration of biochemical alterations in myopathy. Key findings include: 1. **Mitochondrial Preparation**: The preparation of muscle mitochondria from dystrophic and normal mice was detailed, emphasizing the importance of using a sucrose medium for better separation of myofibrils and mitochondria. 2. **Adenosine Triphosphatase (ATPase) Activity**: - **Stimulating Factors**: Dinitrophenol consistently stimulated ATPase activity in the presence of Mg²⁺ ions, with maximum stimulation at a concentration of about 0.1 mm. - **Inhibitors**: Chlorpromazine and atabrine were potent inhibitors of muscle ATPase, while NaF had a weak inhibitory effect. - **Cations**: Mg²⁺, Co²⁺, and Mn²⁺ ions were found to be equally effective in activating ATPase activity, while Ca²⁺ and Fe²⁺ ions were less active. 3. **Succinate-Tetrazolium Reductase Activity**: - **Activity**: Mitochondria from dystrophic and normal muscle showed no significant difference in succinate-tetrazolium reductase activity. - **Reduction Mechanism**: Phenazine methosulphate acted as an intermediate electron carrier, increasing formazan production by acting as a direct acceptor of electrons in the oxidation of succinate. 4. **Discussion**: - The small stimulation of ATPase activity by dinitrophenol in muscle mitochondria contrasts with the larger response observed in liver mitochondria, possibly due to the greater difficulty in preparing undamaged muscle mitochondria. - The slightly higher ATPase activity in dystrophic muscle may explain the reported lowered ATP concentration in these muscles. - The normal succinate-tetrazolium reductase activity in dystrophic muscle mitochondria is of interest given the reported morphological changes in mitochondria. 5. **Conclusion**: - The study highlights the importance of understanding the biochemical changes in muscle diseases, particularly in dystrophic conditions, and provides insights into the biochemistry of human muscular dystrophies.This paper by R. J. Pennington investigates the biochemical abnormalities associated with primary myopathies, particularly focusing on the mitochondrial succinate dehydrogenase and adenosine triphosphatase (ATPase) activities in dystrophic mouse muscle. The study uses a strain of mice with an autosomal recessive gene causing a muscular dystrophy, which has facilitated the exploration of biochemical alterations in myopathy. Key findings include: 1. **Mitochondrial Preparation**: The preparation of muscle mitochondria from dystrophic and normal mice was detailed, emphasizing the importance of using a sucrose medium for better separation of myofibrils and mitochondria. 2. **Adenosine Triphosphatase (ATPase) Activity**: - **Stimulating Factors**: Dinitrophenol consistently stimulated ATPase activity in the presence of Mg²⁺ ions, with maximum stimulation at a concentration of about 0.1 mm. - **Inhibitors**: Chlorpromazine and atabrine were potent inhibitors of muscle ATPase, while NaF had a weak inhibitory effect. - **Cations**: Mg²⁺, Co²⁺, and Mn²⁺ ions were found to be equally effective in activating ATPase activity, while Ca²⁺ and Fe²⁺ ions were less active. 3. **Succinate-Tetrazolium Reductase Activity**: - **Activity**: Mitochondria from dystrophic and normal muscle showed no significant difference in succinate-tetrazolium reductase activity. - **Reduction Mechanism**: Phenazine methosulphate acted as an intermediate electron carrier, increasing formazan production by acting as a direct acceptor of electrons in the oxidation of succinate. 4. **Discussion**: - The small stimulation of ATPase activity by dinitrophenol in muscle mitochondria contrasts with the larger response observed in liver mitochondria, possibly due to the greater difficulty in preparing undamaged muscle mitochondria. - The slightly higher ATPase activity in dystrophic muscle may explain the reported lowered ATP concentration in these muscles. - The normal succinate-tetrazolium reductase activity in dystrophic muscle mitochondria is of interest given the reported morphological changes in mitochondria. 5. **Conclusion**: - The study highlights the importance of understanding the biochemical changes in muscle diseases, particularly in dystrophic conditions, and provides insights into the biochemistry of human muscular dystrophies.