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Query: EC:1.9.3.1 (cytochrome oxidase)
 8,822 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The presence of additional subunits in cytochrome oxidase distinguish the multicellular eukaryotic enzyme from that of a simple unicellular bacterial enzyme. The number of these additional subunits increases with increasing evolutionary stage of the organism. Subunits I-III of the eukaryotic enzyme are related to the three bacterial subunits, and they are encoded on mitochondrial DNA. The additional subunits are nuclear encoded. Experimental evidences are presented here to indicate that the lower enzymatic activity of the mammalian enzyme is due to the presence of nuclear-coded subunits. Dissociation of some of the nuclear-coded subunits (e.g. VIa) by laurylmaltoside and anions increased the activity of the rat liver enzyme to a value similar to that of the bacterial enzyme. Further, it is shown that the intraliposomal nucleotides influence the kinetics of ferrocytochrome c oxidation by the reconstituted enzyme from bovine heart but not from P. denitrificans. The regulatory function attributed to the nuclear-coded subunits of mammalian cytochrome c oxidase is also demonstrated by the tissue-specific response of the reconstituted enzyme from bovine heart but not from bovine liver to intraliposomal ADP. These enzymes from bovine heart and liver differ in the amino acid sequences of subunits VIa, VIIa, and VIII. The results presented here are taken to indicate a regulation of cytochrome c oxidase activity by nuclear-coded subunits which act like receptors for allosteric effectors and influence the catalytic activity of the core enzyme via conformational changes.
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PMID:Evolutionary aspects of cytochrome c oxidase. 164

1. The occurrence of an optimal ionic strength for the steady-state activity of isolated cytochrome aa3 can be attributed to two opposite effects: upon lowering of the ionic strength the affinity between cytochrome c and cytochrome aa3 increases, whereas in the lower ionic strength region the formation of a less active cytochrome c-aa3 complex limits the ferrocytochrome c association to the low affinity site. 2. At low ionic strength, the reduction of cytochrome c-aa3 complex by ferrocytochrome c1 proceeds via non-complex-bound cytochrome c. Under these conditions the positively charged cytochrome c provides the electron transfer between the negatively charged cytochromes c1 and aa3. 3. Polylysine is found to stimulate the release of tightly bound cytochrome c from the cytochrome c-aa3 complex. This property points to the existence of negative cooperativity between the two binding sites. We suggest that the stimulation is not restricted to polylysine, but also occurs with cytochrome c. 4. Dissociation rates of both high and low affinity sites on cytochrome aa3 were determined indirectly. The dissociation constants, calculated on the basis of pre-steady-state reaction rates at an ionic strength of 8.8 mM, were estimated to be 0.6 nM and 20 microM for the high and low affinity site, respectively.
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PMID:Ionic strength effects on cytochrome aa3 kinetics. 626 Jan 60

The albino3 (alb3) mutant of Arabidopsis forms white or light yellow cotyledons and leaves and when germinated on soil does not survive beyond the seedling stage. The chloroplasts of the mutant are abnormal, as determined by electron microscopy, and contain reduced levels of chlorophyll. However, the chloroplasts of alb3 mutants are sufficiently differentiated to enable the expression of two nuclear genes whose transcription requires the presence of chloroplasts. The ALB3 gene was isolated by transposon tagging with the Activator/Dissociation transposable element system. ALB3 is a novel plant gene whose product shows homology to a bacterial membrane protein previously identified in five bacterial species and to a yeast protein, OXA1, and its human homolog. OXA1 is required in the mitochondria for proper assembly of the cytochrome oxidase complex. ALB3 does not have a function identical to OXA1 because mitochondrial cytochrome oxidase activity is not affected in the mutant, and immunogold labeling as well as chloroplast import experiments performed in vitro demonstrated that the ALB3 protein is present in chloroplast membranes. ALB3 might have a function related to that of OXA1 and be involved in the assembly of a chloroplast enzyme complex.
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PMID:ALBINO3, an Arabidopsis nuclear gene essential for chloroplast differentiation, encodes a chloroplast protein that shows homology to proteins present in bacterial membranes and yeast mitochondria. 916 49

Mitochondria execute key pathways of central metabolism and serve as cellular sensing and signaling entities, functions that depend upon interactions between mitochondrial and nuclear genetic systems. This is exemplified in cytoplasmic male sterility type S (CMS-S) of Zea mays, where novel mitochondrial open reading frames are associated with a pollen collapse phenotype, but nuclear restorer-of-fertility (restorer) mutations rescue pollen function. To better understand these genetic interactions, we screened Activator-Dissociation (Ac-Ds), Enhancer/Suppressor-mutator (En/Spm), and Mutator (Mu) transposon-active CMS-S stocks to recover new restorer mutants. The frequency of restorer mutations increased in transposon-active stocks compared to transposon-inactive stocks, but most mutants recovered from Ac-Ds and En/Spm stocks were unstable, reverting upon backcrossing to CMS-S inbred lines. However, 10 independent restorer mutations recovered from CMS-S Mu transposon stocks were stable upon backcrossing. Many restorer mutations condition seed-lethal phenotypes that provide a convenient test for allelism. Eight such mutants recovered in this study included one pair of allelic mutations that were also allelic to the previously described rfl2-1 mutant. Targeted analysis of mitochondrial proteins by immunoblot identified two features that consistently distinguished restored CMS-S pollen from comparably staged, normal-cytoplasm, nonmutant pollen: increased abundance of nuclear-encoded alternative oxidase relative to mitochondria-encoded cytochrome oxidase and decreased abundance of mitochondria-encoded ATP synthase subunit 1 compared to nuclear-encoded ATP synthase subunit 2. CMS-S restorer mutants thus revealed a metabolic plasticity in maize pollen, and further study of these mutants will provide new insights into mitochondrial functions that are critical to pollen and seed development.
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PMID:Restorer-of-Fertility Mutations Recovered in Transposon-Active Lines of S Male-Sterile Maize. 2916 73