Vielhaber 2000 Biochem Soc Trans
|Vielhaber S, Kudin A, Schroder R, Elger CE, Kunz WS (2000) Muscle fibres: applications for the study of the metabolic consequences of enzyme deficiencies in skeletal muscle. Biochem Soc Trans 28:159-64.|
Abstract: Mitochondrial function in saponin-permeabilized muscle fibres can be studied by high-Resolution respirometry, laser-excited fluorescence spectroscopy and fluorescence microscopy. We applied these techniques to study metabolic effects of changes in the pattern of mitochondrial enzymes in skeletal muscle of patients with chronic progressive external ophthalmoplegia or Kearns± Sayre syndrome harbouring large-scale deletions of mitchondrial DNA (mtDNA). In all patients combined deficiencies of respiratory chain enzymes containing mitochondrially encoded subunits were observed. The citrate synthase-normalized activity ratios of these enzymes decreased linearly with increasing mtDNA heteroplasmy. This indicates the absence of any well-defined mutation thresholds for mitochondrial enzyme activities in the entire skeletal muscle. We applied metabolic control analysis to perform a quantitative estimation of the metabolic influence of the observed enzyme deficiencies. For patients with degrees of mtDNA heteroplasmy below about 60% we observed at almost normal maximal rates of respiration an increase in flux control coeficients of Complexes I and CIV. Permeabilized skeletal-muscle fibres of patients with higher degrees of mtDNA heteroplasmy and severe enzyme deficiencies exhibited additionally decreased maximal rates of respiration. This finding indicates the presence of a `metabolic threshold' which can be assessed by functional studies of muscle fibres providing the link to the phenotypic expression of the mtDNA mutation in skeletal muscle.
• Keywords: Genotype, Phenotype relations, Mitochondrial (mt) myopathy, mtDNA deletion
Labels: MiParea: Respiration, mtDNA;mt-genetics, mt-Medicine, Patients Pathology: Inherited
Organism: Human Tissue;cell: Skeletal muscle Preparation: Permeabilized tissue Enzyme: Complex I, Complex IV;cytochrome c oxidase, Marker enzyme Regulation: Flux control, Threshold;excess capacity