Immunochemical study of subunit VI (Mr 13,400) of mitochondrial ubiquinol-cytochrome c reductase

Usui, Shigeyuki; Yu, Linda; Harmon, James

doi:10.1016/0003-9861(91)90449-s

Cited by 5 publications

(4 citation statements)

References 33 publications

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“…In the bovine heart enzyme the complex had to be delipidated prior to incubation with the antibodies, indicating that the catalytic-site-related epitopes are not exposed when phospholipid is present, which seems to be in contrast with the situation in yeast. From their results the authors concluded that the 14-kDa subunit faces the matrix side of the enzyme, which is in agreement with the results obtained by our group [26], and that it is not involved in the Q," site [25], but in the Qo,, site Previously Schoppink et al [20] showed that the pleiotropic properties of the QCR7" mutation could be relieved by a wild-type gene replacement but no systematic efforts were made to establish an episomal system. To study the effect on complex I11 of transformation of a QCR7" strain with in vitro mutagenised QCR7 genes we decided to develop such a system.…”

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confidence: 89%

“…Since this association is prevented in the QCR7', the QCR8' and the cytochrome b mutants, the remainder of the cytochrome b subcomplex is degraded when either of these subunits is missing [22, 231. The pleiotropic effects, caused by the disruption of the QCR7 gene, preclude analysis of the possible mechanistic involvement of this subunit in the activity of the enzyme. Indications of an involvement of the 34-kDa subunits in the activity of the bc, complexes of yeast [24] and beef-heart [25] came from studies using specific antibodies directed against these subunits. It was shown that these antibodies were able to inhibit complex I11 activity.…”

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confidence: 99%

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The C‐terminus of the 14‐kDa subunit of ubiquinol‐cytochrome‐c oxidoreductase of the yeast Saccharomyces cerevisiae is involved in the assembly of a functional enzyme

Hemrika

Jong

Berden

et al. 1994

European Journal of Biochemistry

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Disruption of QCR7, the gene encoding the 14-kDa subunit of ubiquinol-cytochrome-c oxidoreductase of the yeast Saccharomyces cerevisiae, results in an inactive enzyme which lacks holocytochrome b and has severely reduced levels of apo-cytochrome b, the Rieske Fe-S protein and the 11-kDa subunit [Schoppink, P. J., Berden, J. Eul: J. Biochem. 181, An episomal system was developed to study the effect on complex I11 of transformation of in vitro mutagenised QCR7 genes to a QCR7' mutant. Transformation of a gene ( T N T l ) in which the 12 C-terminal residues are replaced by 3 amino acids encoded by an oligonucleotide containing a stop codon in all three reading frames (STOP-oligonucleotide), only leads to partial complementation of the respiratory capacity of the yeast strain. The amounts of apo-cytochrome 6 , the Rieske Fe-S protein and the 11 -kDa subunit are reduced and enzymic activity, together with the amount of holo-cytochrome b, is lowered to about 40% of that of the wild type, indicating a normal turnover number of the mutant enzyme.Transformation of the QCR7" mutant with another gene (TNT2) encoding the first 96 residues of the 14-kDa subunit fused to 9 amino acids encoded by the STOP-oligonucleotide, leads to a phenotype almost indistinguishable from that of the QCR7" mutant.The role of the charged C-terminus of the 14-kDa (and the 11-kDa) subunit in the assembly of a functional complex 111 is discussed.Ubiquinol-cytochrome-c oxidoreductase (complex I11 or the be, complex) is an oligomeric respiratory-chain enzyme, which invariably consists of at least three subunits: cytochrome b, cytochrome c, and the Rieske Fe-S subunit. These subunits, which carry the prosthetic groups, are functionally well characterised and have been shown to be essential for the activity of the enzyme. Fully active three-subunit be, complexes can be isolated from bacteria such as Paracoccus denitrficans and Rhodospirillum rubrum [1, 21. All known eukaryotic bc, complexes contain additional subunits, implying a more complicated situation in these cases, but in spite of a great deal of experimental effort the precise physiological role of these extra subunits remains enigmatic ( [ 3 , 41 and references therein). The bc, complex of the yeast Saccharomyces cerevisiae contains six or seven additional subunits which are named, in order of descending molecular mass the 44-, 40-(also called core I and core I1 subunits), 17-,

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confidence: 89%

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confidence: 99%

The C‐terminus of the 14‐kDa subunit of ubiquinol‐cytochrome‐c oxidoreductase of the yeast Saccharomyces cerevisiae is involved in the assembly of a functional enzyme

Hemrika

Jong

Berden

et al. 1994

European Journal of Biochemistry

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“…Originally, this protein was called a "ubiquinone-binding protein" because it was thought to bind arylazido ubiquinone derivatives upon photoaffinity labeling (Yu and Yu, 1982;Yu et al, 1986). Later, a slightly smaller subunit with different properties was identified as the labeled protein (Usui et al, 1991; bovine subunit VII, 9.5 kD). Therefore, we refer to the bovine 13.4-kD subunit and the yeast 14.4-kD subunit as the "14-kD protein" of Cyt c reductase.…”

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confidence: 99%

“…The 14-kD protein of Cyt c reductase from yeast and bovine is located on the matrix side of the enzyme complex as shown with antibodies directed against the subunit (Japa et a]., 1987;Hemrika and Berden, 1990;Usui et al, 1991). Mutations of Cyt b affect the steady-state leve1 of the 14-kD protein together with an 11-kD subunit in yeast (de Haan et al, 1984).…”

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Molecular Features and Mitochondrial Import Pathway of the 14-Kilodalton Subunit of Cytochrome c Reductase from Potato

Braun

Schmitz

1995

Plant Physiol.

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The cytochrome c reductase complexes from fungi and mammals both contain a 14-kD protein (yeast, 14.4 kD; bovine, 13.4 kD) that does not directly participate in electron transfer but possibly is indirectly involved in the function of the complex and has a role in assembly of the multimeric enzyme. A subunit of comparable size was identified for the bc, complex of higher plants. The 14-kD protein from potato (Solanum tuberosum) was specifically separated from the isolated protein complex in the presence of 6 M urea and is, therefore, assumed to be a peripheral component. Direct sequence analysis of the proteins from potato and wheat (Triticum aestivum) and isolation of corresponding cDNA clones for the subunit from potato revealed clear similaríty to the equivalent proteins from yeast and bovine. The wheat 14-kD protein seems to occur in two isoforms. The 14-kD protein from plants is very hydrophilic, has a characteristic charge distribution, and contains no potential membrane-spanning helices. In vitro import of the radiolabeled 14-kD protein from potato into isolated mitochondria depends on the membrane potential across the inner mitochondrial membrane. The protein seems to lack a cleavable mitochondrial presequence, because it is not processed upon translocation. Possible intramolecular regions involved in targeting of the 14-kD protein to plant mitochondria are discussed.The mitochondriaI bc, complex (EC 1.10.2.2.) is the middle segment of the respiratory chain and catalyzes the reduction of Cyt c by the oxidation of ubiquinol. Coupled with this reaction it contributes to the chemiosmotic gradient across the inner mitochondrial membrane by translocating protons from the matrix to the intermembrane space. In fungi and mammals the Cyt c reductase is an oligomeric protein complex comprising 9 to 11 subunits (reviewed by Trumpower, 1990; Bechmann et al., 1992): two large "core" proteins, three respiratory proteins that directly participate in electron transport (Cyt b, Cyt cl, and the "Rieske" iron sulfur protein), and four to six small proteins with molecular masses of less than 20 kD. Since bacterial bc, complexes that contain only the respiratory subunits have the same activity as the eukaryotic enzymes (Trumpower, 19901, the role of the supplementary subunits is not quite understood. One of them is the bovine subunit VI (13.4 kD), which was shown to be similar to subunit VI1 This work was supported by the Deutsche Forschungsgemein-

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Mutational Studies of the Cytochrome bc1 Complexes

Gray

Daldal

Advances in Photosynthesis and Respiration

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Immunochemical study of subunit VI (Mr 13,400) of mitochondrial ubiquinol-cytochrome c reductase

Cited by 5 publications

References 33 publications

The C‐terminus of the 14‐kDa subunit of ubiquinol‐cytochrome‐c oxidoreductase of the yeast Saccharomyces cerevisiae is involved in the assembly of a functional enzyme

The C‐terminus of the 14‐kDa subunit of ubiquinol‐cytochrome‐c oxidoreductase of the yeast Saccharomyces cerevisiae is involved in the assembly of a functional enzyme

Molecular Features and Mitochondrial Import Pathway of the 14-Kilodalton Subunit of Cytochrome c Reductase from Potato

Mutational Studies of the Cytochrome bc1 Complexes

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