Abstract
Mitochondrial NADH:ubiquinone oxidoreductase (complex I) from bovine heart is a complicated multisubunit, membrane-bound assembly. Seven subunits are encoded by mitochondrial DNA, and the sequences of 36 nuclear encoded subunits have been described. The subunits of complex I and two subcomplexes (Ialpha and Ibeta) were resolved on one- and two-dimensional gels and by reverse-phase high performance liquid chromatography. Mass spectrometric analysis revealed two previously unknown subunits in complex I, named B14.7 and ESSS, one in each subcomplex. Coding sequences for each protein were identified in data bases and were confirmed by cDNA cloning and sequencing. Subunit B14.7 has an acetylated N terminus, no presequence, and contains four potential transmembrane helices. It is homologous to subunit 21.3b from complex I in Neurospora crassa and is related to Tim17, Tim22, and Tim23, which are involved in protein translocation across the inner membrane. Subunit ESSS has a cleaved mitochondrial import sequence and one potential transmembrane helix. A total of 45 different subunits of bovine complex I have now been characterized.
Highlights
Mitochondrial NADH:ubiquinone oxidoreductase from bovine heart is a complicated multisubunit, membrane-bound assembly
This paper describes the extensive re-investigation of the nuclear encoded subunit composition of bovine complex I
Subunit B14.7 has an acetylated N terminus. It is a homologue of subunit 21.3b in complex I from N. crassa [21] and is related to three proteins, Tim17, Tim22, and Tim23, which are involved in protein translocation across the inner mitochondrial membrane [22, 23]
Summary
Mitochondrial NADH:ubiquinone oxidoreductase (complex I) from bovine heart is a complicated multisubunit, membrane-bound assembly. It is homologous to subunit 21.3b from complex I in Neurospora crassa and is related to Tim, Tim, and Tim, which are involved in protein translocation across the inner membrane. NADH:ubiquinone oxidoreductase (complex I) from the inner membrane of bovine heart mitochondria is a multisubunit, membrane-bound, L-shaped assembly with a molecular mass of over 900 kDa [1,2,3]. Subunit B14.7 has an acetylated N terminus It is a homologue of subunit 21.3b in complex I from N. crassa [21] and is related to three proteins, Tim, Tim, and Tim, which are involved in protein translocation across the inner mitochondrial membrane [22, 23]. Subunits B14.7 and ESSS of Bovine Complex I mature subunit ESSS, which is homologous to human neuronal protein NP17.3 [24]
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