Resumo

FERREIRA, Mariana; AGUIAR, Tatiana  e  VILARINHO, Laura. Mitochondrial Respiratory Chain. Arq Med [online]. 2008, vol.22, n.2-3, pp.49-56. ISSN 2183-2447.

Mitochondrial cytopathies are a group of genetically heterogeneous disorders, that is characterized by alterations in the mitochondrial structure and oxidative phosphorylation deficiency (OXPHOS). OXPHOS system consists of five multimeric protein complexes and two electron carriers. NADH-ubiquinone oxidoreductase (complex I), the first and largest of the five complexes, is the major entry point of electrons, from Krebs cycle, of the OXPHOS system. Complex I deficiency is a frequently diagnosed defect of the mitochondrial OXPHOS system, caused by mutations in either the mitochondrial DNA (mtDNA) or the nuclear DNA. Because of this dual genetic control, which contributes to the complexity of the OXPHOS system, defects on complex I results in a broad spectrum of clinical phenotypes, that are usually associated to severe metabolic disorders of childhood, including progressive cardiomyopathy, encephalomyopathy, leukodystrophy or Leigh syndrome. Research on the mechanisms underlying mitochondrial complex I deficiency has used several models, such as Neurospora crassa and human cell cybrids, and has taken advantage by the routinary use of novel biochemical tools, such as Blue Native Polyacrylamide gel electrophoresis. Given the complexity of this OXPHOS enzyme, both in structure and maintenance, it is difficult to achieve the molecular diagnosis of patients in a routine basis. In Portugal, the study of these patients did not go beyond the biochemical activity measurements of respiratory chain enzymes and screening of most common point mutations and rearrangements of mtDNA, until some months ago. As a consequence, at the molecular level, the majority of the complex I deficiency cases remain unsolved, being essential to move forward to a more wide-ranging study. Moreover, a correct diagnosis will permit adequate genetic counselling and prenatal diagnosis.

Palavras-chave : OXPHOS; complex I; mtDNA; MRC; nDNA; mitochondrial disorders.

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