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Mol. Cell. Biol., 03 1996, 771-777, Vol 16, No. 3
AS Jun, IA Trounce, MD Brown, JM Shoffner and DC Wallace
A heteroplasmic G-to-A transition at nucleotide pair (np) 14459 within the
mitochondrial DNA (mtDNA)-encoded NADH dehydrogenase subunit 6 (ND6) gene
has been identified as the cause of Leber hereditary optic neuropathy
(LHON) and/or pediatric-onset dystonia in three unrelated families. This
ND6 np 14459 mutation changes a moderately conserved alanine to a valine at
amino acid position 72 of the ND6 protein. Enzymologic analysis of
mitochondrial NADH dehydrogenase (complex I) with submitochondrial
particles isolated from Epstein-Barr virus- transformed lymphoblasts
revealed a 60% reduction (P < 0.005) of complex I-specific activity in
patient cell lines compared with controls, with no differences in enzymatic
activity for complexes II plus III, III and IV. This biochemical defect was
assigned to the ND6 np 14459 mutation by using transmitochondrial cybrids
in which patient Epstein-Barr virus-transformed lymphoblast cell lines were
enucleated and the cytoplasts were fused to a mtDNA-deficient (p 0)
lymphoblastoid recipient cell line. Cybrids harboring the np 14459 mutation
exhibited a 39% reduction (p < 0.02) in complex I-specific activity
relative to wild-type cybrid lines but normal activity for the other
complexes. Kinetic analysis of the np 14459 mutant complex I revealed that
the Vmax of the enzyme was reduced while the Km remained the same as that
of wild type. Furthermore, specific activity was inhibited by increasing
concentrations of the reduced coenzyme Q analog decylubiquinol. These
observations suggest that the np 14459 mutation may alter the coenzyme
Q-binding site of complex I.
Copyright © 1996, American Society for Microbiology
Use of transmitochondrial cybrids to assign a complex I defect to the mitochondrial DNA-encoded NADH dehydrogenase subunit 6 gene mutation at nucleotide pair 14459 that causes Leber hereditary optic neuropathy and dystonia
Department of Genetics and Molecular Medicine, Emory University School of Medicine, Atlanta, Georgia, USA.
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