title: Import rate of the E1beta subunit of human branched chain alpha-ketoacid dehydrogenase is a limiting factor in the amount of complex formed in the mitochondria.
abstract: Components of the mitochondrial branched chain alpha-ketoacid dehydrogenase multienzyme complex are all encoded by nuclear genes. The functional complex is formed with a known stoichiometric relationship of subunits, but how they enter the mitochondria and form the complex is not defined. Although cytosolic precursors for several of the proteins have been identified, the requirements for import and processing have not been described. Here we demonstrate the similar requirements for in vitro import and processing of the three catalytic subunits unique the this complex. Import was not affected by the amount of endogenous BCKD within the mitochondria. No cooperativity or competition among the subunits for import was found when subunits were used in combination. The relative rates of entry are E1alpha>E2>/=E1beta, making E1beta the limiting component supporting previously reported observations.
authors.affiliation: Department of Genetics, Emory University School of Medicine, 1462 Clifton Road, Room 446, Atlanta, GA 30322, USA.
authors.forename: T L
authors.initials: TL
authors.lastname: Sitler
authors.forename: M C
authors.initials: MC
authors.lastname: McKean
authors.forename: F
authors.initials: F
authors.lastname: Peinemann
authors.forename: E
authors.initials: E
authors.lastname: Jackson
authors.forename: D J
authors.initials: DJ
authors.lastname: Danner
mesh_terms: D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide); D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D017123:Bacteriophage T7 / Q000235:genetics; D001692:Biological Transport; D004259:DNA-Directed DNA Polymerase / Q000235:genetics; D006801:Humans; D007658:Ketone Oxidoreductases / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D051379:Mice; D008930:Mitochondria, Liver / Q000201:enzymology*; D009097:Multienzyme Complexes / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D011498:Protein Precursors / Q000096:biosynthesis / Q000235:genetics
chemical_list: D009097:Multienzyme Complexes; D011498:Protein Precursors; D000255:Adenosine Triphosphate; D007658:Ketone Oxidoreductases; D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide); C034970:bacteriophage T7 induced DNA polymerase; D004259:DNA-Directed DNA Polymerase