PubMed · 13140088
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T BRUCE. 1953. [Pulmonary function and collapse therapy].. https://pubmed.ncbi.nlm.nih.gov/13140088/
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Cytochrome c peroxidase (CcP) uses hydrogen peroxide as an electron acceptor to oxidize cytochrome c (Cc) in the mitochondrial intermembrane space. A null allele of yeast CCP1 gene encoding CcP was created by one-step gene disruption method in a diploid yeast strain. Haploid yeast cells with the disrupted CCP1 gene were viable and able to grow in a medium containing lactic acid or glycerol as an energy source, indicating that CcP is not essential for both cell viability and respiration. However, CCP1-disrupted cells were more sensitive to H2O2 than wild-type cells. We also constructed a CCP1-lacZ fused gene and integrated this gene into yeast chromosomal DNA to monitor the expression of CCP1 gene. We found that expression of CCP1 gene increases under respiratory culture conditions and by treatments with H2O2. These results hint that the biological function of CcP is to reduce H2O2 generated during aerobic respiratory process. Moreover, expression of CCP1 gene increased by treatments with peroxynitrite, indicating that CcP may act as a peroxynitrite scavenger.
Corynebacterium glutamicum is an aerobic bacterium that requires oxygen as exogenous electron acceptor for respiration. Recent molecular and biochemical analyses together with information obtained from the genome sequence showed that C. glutamicum possesses a branched electron transport chain to oxygen with some remarkable features. Reducing equivalents obtained by the oxidation of various substrates are transferred to menaquinone via at least eight different dehydrogenases, i.e. NADH dehydrogenase, succinate dehydrogenase, malate:quinone oxidoreductase, pyruvate:quinone oxidoreductase, D-lactate dehydrogenase, L-lactate dehydrogenase, glycerol-3-phosphate dehydrogenase and L-proline dehydrogenase. All these enzymes contain a flavin cofactor and, except succinate dehydrogenase, are single subunit peripheral membrane proteins located inside the cell. From menaquinol, the electrons are passed either via the cytochrome bc(1) complex to the aa(3)-type cytochrome c oxidase with low oxygen affinity, or to the cytochrome bd-type menaquinol oxidase with high oxygen affinity. The former branch is exceptional, in that it does not involve a separate cytochrome c for electron transfer from cytochrome c(1) to the Cu(A) center in subunit II of cytochrome aa(3). Rather, cytochrome c(1) contains two covalently bound heme groups, one of which presumably takes over the function of a separate cytochrome c. The bc(1) complex and cytochrome aa(3) oxidase form a supercomplex in C. glutamicum. The phenotype of defined mutants revealed that the bc(1)-aa(3) branch, but not the bd branch, is of major importance for aerobic growth in minimal medium. Changes of the efficiency of oxidative phosphorylation caused by qualitative changes of the respiratory chain or by a defective F(1)F(0)-ATP synthase were found to have strong effects on metabolism and amino acid production. Therefore, the system of oxidative phosphorylation represents an attractive target for improving amino acid productivity of C. glutamicum by metabolic engineering.
Mature and old growth trees of varying sapwood thickness were compared with regard to stem respiration. An increment core-based, laboratory method under controlled temperature was used to measure tissue-level respiration (termed respiratory potential) of ten different tree species. Bark (dead outer and live inner combined), sapwood, and heartwood thickness measurements were used to predict sapwood volume from stem diameter (including bark) for four of the ten species. These predictions of sapwood volume were used to scale respiratory potential to the main-bole level (excluding all branches). On the core level, species that maintained narrow sapwood (8-16% of bole radius) such as Pseudotusga menziesii, Taxus brevifolia, and Thuja plicata, had sapwood respiratory potentials in the lower bole that were 50% higher (P<0.05) than species with wide sapwood (>16% of bole radius), such as Abies amabilis, Pinus monticola, and Tsuga heterophylla. This pattern was not observed for inner bark respiratory potential, or for sapwood respiratory potential within the crown. On the main-bole level, respiratory potential per unit volume was inversely correlated to the live bole volumetric fraction (inner bark plus sapwood divided by whole bole volume) (Adj. R(2)=0.6). Specifically, tree species with 18-20% of the main bole alive potentially respired 1.3-3 times more per unit live bole volume than species with over 40%, suggesting that the live bole was less metabolically active in tree species that maintained large volumes of sapwood.