Analysis of the Subunit Composition of Complex I from Bovine Heart Mitochondria*S

Abstract

Complex I purified from bovine heart mitochondria is a multisubunit membrane-bound assembly. In the past, seven of its subunits were shown to be products of the mitochondrial genome, and 35 nuclear encoded subunits were identified. The complex is L-shaped with one arm in the plane of the membrane and the other lying orthogonal to it in the mitochondrial matrix. With mildly chaotropic detergents, the intact complex has been resolved into various subcomplexes. Subcomplex Ilambda represents the extrinsic arm, subcomplex Ialpha consists of subcomplex Ilambda plus part of the membrane arm, and subcomplex Ibeta is another substantial part of the membrane arm. The intact complex and these three subcomplexes have been subjected to extensive reanalysis. Their subunits have been separated by three independent methods (one-dimensional SDS-PAGE, two-dimensional isoelectric focusing/SDS-PAGE, and reverse phase high pressure liquid chromatography (HPLC)) and analyzed by tryptic peptide mass fingerprinting and tandem mass spectrometry. The masses of many of the intact subunits have also been measured by electrospray ionization mass spectrometry and have provided valuable information about post-translational modifications. The presence of the known 35 nuclear encoded subunits in complex I has been confirmed, and four additional nuclear encoded subunits have been detected. Subunits B16.6, B14.7, and ESSS were discovered in the SDS-PAGE analysis of subcomplex Ilambda, in the two-dimensional gel analysis of the intact complex, and in the HPLC analysis of subcomplex Ibeta, respectively. Despite many attempts, no sequence information has been obtained yet on a fourth new subunit (mass 10,566+/-2 Da) also detected in the HPLC analysis of subcomplex Ibeta. It is unlikely that any more subunits of the bovine complex remain undiscovered. Therefore, the intact enzyme is a complex of 46 subunits, and, assuming there is one copy of each subunit in the complex, its mass is 980 kDa.

Respiratory-deficient mutants of the unicellular green alga Chlamydomonas: A review

“…This suggests that ND4, ND5 and PSDW, on one hand, and ND1, ND3, ND4L, and ND6, on the other hand, are located in two different membrane domains of the complex I membrane arm. This hypothesis is in good agreement with structural models proposed for the localization of these subunits within for example Arabidopsis [9] or bovine complex I [49].…”

Assembly factors for the membrane arm of human complex I

“…For each two electrons transferred from NADH to ubiquinone, four protons are ejected from the mitochondrial matrix, thereby contributing to the proton motive force across the inner membrane (1). The mammalian enzyme has 44 subunits, with a combined molecular mass of about 1 MDa, assembled into an L-shaped complex, with one arm embedded in the inner membrane and the other protruding into the matrix of the organelle (2)(3)(4). Seven hydrophobic subunits (ND1-ND6 and ND4L) of the membrane arm of NADH dehydrogenase (complex I) are encoded in mitochondrial DNA, and synthesized on mitochondrial ribosomes (5).…”

Atividade farmacológica da monocrotalina isolada de plantas do gênero Crotalaria

“…A transferência de elétrons pelo NADH (oxidação) via complexo I reduz a ubiquinona (coenzima Q) gerando parte do gradiente eletroquímico requerido pela síntese de ATP. Contudo, a inibição do complexo I da cadeia respiratória pode constituir um importante mecanismo de deleção do ATP da célula e assim levar a morte celular (Lenaz et al, 2006;Caroll et al, 2003).…”