Abstract
The brindled mottled mouse (Mobr), an animal model of the Menkes' copper deficiency syndrome, was used for the investigation of changes in respiratory flux control associated with cytochrome c oxidase deficiency in muscle. Enzymatic analysis of cardiac and skeletal muscles showed an approximately 2-fold decrease in cytochrome c oxidase activity of brindled mutants in both types of muscles as compared with controls. The activities of NADH-cytochrome c oxidoreductase (respiratory chain segment I-III) and succinate-cytochrome c oxidoreductase (segment II-III) were normal. Assessment of mitochondrial respiratory function was performed using chemically skinned musculus quadriceps or heart muscle fibers isolated from control and brindled mottled mice. In skeletal muscle, there was no difference found in maximal rates of respiration. In the Mobr hearts, this parameter was slightly lower than control. Alternately, the determination of flux control coefficients of cytochrome c oxidase performed by a step by step inhibition of respiration with increasing concentrations of azide or cyanide revealed significantly sharper inhibition curves for brindled mice than for control, indicating more than 2-fold elevated flux control coefficients of cytochrome c oxidase. This investigation proved essential in characterizing the metabolic effect of a cytochrome c oxidase deficiency. We conclude, therefore, that application of metabolic control analysis can be a valuable approach to study defects of mitochondrial oxidative phosphorylation.
Highlights
The brindled mouse is a variant of the X-linked mottled mutants (Mobr) with severe copper deficiency and is considered to be an animal model of Menkes’ syndrome (Menkes’ kinky hair disease) [1,2,3,4,5]
It was suggested that the lower level of energy metabolism caused by the decrease in both copper concentration and cytochrome c oxidase activity may be responsible for brain degeneration associated with the Menkes’ disease [6, 11]
Measurements of maximal rates of mitochondrial respiration are often used for the functional determination of the different mitochondrial defects [12,13,14]
Summary
Animals—Five mottled brindled mutant male mice (Mobr) obtained from Genetic Division MRC Radiobiology Unit (Chilton, DIDCOT Oxon OX11 ORD, United Kingdom) and five normal controls were used to study mitochondrial and enzymatic properties of cardiac and skeletal (quadriceps) muscles. Animals were euthanized by cervical dislocation, hearts and m. Quadriceps portions revealed 40 Ϯ 3% slow oxidative fibers (succinate dehydrogenase staining). No difference between Mobr quadriceps and control quadriceps muscles using myosin ATPase and succinate dehydrogenase staining was detected. Isolation of Skinned Fibers—The bundles of muscle fibers were isolated from heart (left ventricle) or skeletal muscle
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