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PubMed1988

Evidence for the existence of tissue specific isoenzymes of mitochondrial NADH dehydrogenase.

Mitochondrial NADH dehydrogenase from a variety of rat tissues was isolated by immunoprecipitation with an antiserum to the bovine heart enzyme. The subunit composition of the enzyme from liver, kidney and lung differed from that present in heart, brain and skeletal muscle by the absence of an Mr 18,500 protein and the absence of an Mr 17,000 protein, suggesting the existence of tissue-specific isoenzymes.

Animals↗
PubMed1989

NADH- and NADPH-linked aquacobalamin reductases occur in both mitochondrial and microsomal membranes of rat liver.

To elucidate the mechanism for the synthesis of the coenzyme forms of cobalamin in mammals, rat liver aquacobalamin reductase was partially characterized. Rat liver contained both NADH- and NADPH-linked aquacobalamin reductases. The NADH-linked enzyme was distributed in the mitochondria (approx. 40%) and microsomes (60%), identical to the distribution of the NADPH-linked enzyme. The two mitochondrial NADH- and NADPH-linked enzymes were located inside of the outer membrane.

Animals↗
PubMed2000

Dynamics of the mitochondrial reticulum in live cells using Fourier imaging correlation spectroscopy and digital video microscopy.

We report detailed studies of the dynamics of the mitochondrial reticulum in live cells using two independent experimental techniques: Fourier imaging correlation spectroscopy and digital video fluorescence microscopy. When both methods are used to study the same system, it is possible to directly compare measurements of preaveraged statistical dynamical quantities with their microscopic counterparts. This approach allows the underlying mechanism of the observed rates to be determined. Our results indicate that the dynamics of the reticulum structure is composed of two independent contributions, each important on very different time and length scales. During short time intervals (1-15 sec), local regions of the reticulum primarily undergo constrained thermally activated motion. During long time intervals (>15 sec), local regions of the reticulum undergo long-range "jump" motions that are associated with the action of cytoskeletal filaments. Although the frequency of the jumps depend on the physiological state of the cells, the average jump distance ( approximately 0.8 microm) is unaffected by metabolic activity. During short time intervals, the dynamics appear to be spatially heterogeneous, whereas the cumulative effect of the infrequent jumps leads to the appearance of diffusive motion in the limit of long time intervals.

Biophysical Phenomena↗
PubMed2000

Angular dependences of perpendicular and parallel mode electron paramagnetic resonance of oxidized beef heart cytochrome c oxidase.

Cytochrome c oxidase catalyzes the reduction of oxygen to water with a concomitant conservation of energy in the form of a transmembrane proton gradient. The enzyme has a catalytic site consisting of a binuclear center of a copper ion and a heme group. The spectroscopic parameters of this center are unusual. The origin of broad electron paramagnetic resonance (EPR) signals in the oxidized state at rather low resonant field, the so-called g' = 12 signal, has been a matter of debate for over 30 years. We have studied the angular dependence of this resonance in both parallel and perpendicular mode X-band EPR in oriented multilayers containing cytochrome c oxidase to resolve the assignment. The "slow" form and compounds formed by the addition of formate and fluoride to the oxidized enzyme display these resonances, which result from transitions between states of an integer-spin multiplet arising from magnetic exchange coupling between the five unpaired electrons of high spin Fe(III) heme a(3) and the single unpaired electron of Cu(B). The first successful simulation of similar signals observed in both perpendicular and parallel mode X-band EPR spectra in frozen aqueous solution of the fluoride compound of the closely related enzyme, quinol oxidase or cytochrome bo(3), has been reported recently (Oganesyan et al., 1998, J. Am. Chem. Soc. 120:4232-4233). This suggested that the exchange interaction between the two metal ions of the binuclear center is very weak (|J| approximately 1 cm(-1)), with the axial zero-field splitting (D approximately 5 cm(-1)) of the high-spin heme dominating the form of the ground state. We show that this model accounts well for the angular dependences of the X-band EPR spectra in both perpendicular and parallel modes of oriented multilayers of cytochrome c oxidase derivatives and that the experimental results are inconsistent with earlier schemes that use exchange coupling parameters of several hundred wavenumbers.

Animals↗
PubMed1996

The effect of mild trypsin digestion of F1 on energy coupling in the mitochondrial ATP synthase.

Mild trypsin digestion of isolated bovine-heart mitochondrial F1-ATPase removed the first 15 residues from the N-terminus of subunit alpha under conditions in which other F1 subunits were apparently untouched. When the trypsinized F1 (TF1) was reconstituted with the F0 sector in the mitochondrial membrane (USMP), the ATP hydrolase activity acquired oligomycin sensitivity but ATP hydrolysis was decoupled from proton pumping. TF1 added to USMP did not block the proton channel in F0 as the native F1 did. AMP-PNP inhibited proton conductivity in reconstituted F1-USMP but this effect was lost in reconstituted TF1-USMP. These results indicate that the N-terminus of the F1 alpha subunit plays a critical role in the conformational communication between F1 and F0.

Adenosine Triphosphate↗
PubMed1997

Submitochondrial distributions and stabilities of subunits 4, 5, and 6 of yeast cytochrome oxidase in assembly defective mutants.

The concentration and submitochondrial distribution of the subunit polypeptides of cytochrome oxidase have been studied in wild type yeast and in different mutants impaired in assembly of this respiratory complex. All the subunit polypeptides of the enzyme are associated with mitochondrial membranes of wild type cells, except for a small fraction of subunits 4 and 6 that is recovered in the soluble protein fraction of mitochondria. Cytochrome oxidase mutants consistently display a severe reduction in the steady-state concentration of subunit 1 due to its increased turnover. As a consequence, most of subunit 4, which normally is associated with subunit 1, is found in the soluble fraction. A similar shift from membrane-bound to soluble subunit 6 is seen in mutants blocked in expression of subunit 5a. In contrast, null mutations in COX6 coding for subunit 6 promote loss of subunit 5a. The absence of subunit 5a in the cox6 mutant is the result of proteolytic degradation rather than regulation of its expression by subunit 6. The possible role of the ATP-dependent proteases Rca1p and Afg3p in proteolysis of subunits 1 and 5a has been assessed in strains with combined mutations in COX6, RCA1, and/or AFG3. Immunochemical assays indicate that another protease(s) must be responsible for most of the proteolytic loss of these proteins.

Adenosine Triphosphatases↗
PubMed1998

Mitochondria and cells produce reactive oxygen species in virtual anaerobiosis: relevance to ceramide-induced apoptosis.

Observations of apoptosis in virtual anaerobiosis have raised doubts on the significance of reactive oxygen species in the cascade of events of programmed cell death. This work presents evidence that cells and mitochondrial preparations produce similar levels of hydrogen peroxide under either aerobic or virtually anaerobic conditions. These levels are relevant to the increased production of radicals induced by a ceramide analog that promotes apoptosis. This ceramide acts at center o of mitochondrial complex III.

Anaerobiosis↗
PubMed1988

The presequence of yeast 5-aminolevulinate synthase is not required for targeting to mitochondria.

A truncated form of the yeast mitochondrial 5-aminolevulinate (ALA) synthase was constructed by deletion of the first 75 amino acid residues of its precursor form. This truncated ALA synthase which lost its entire presequence and 40 residues of the mature part possesses a new amino terminus quite different from a typical mitochondrial presequence. This modified protein expressed in vivo is found entirely located within mitochondria. Although it was now unable to reach the matrix space, it was internalized as shown by its resistance to protease in isolated mitochondria. Pulse-chase radiolabeling in the presence of an uncoupler suggests that a membrane potential is not required for the targeting of this truncated ALA synthase. Thus, the amino-terminal signal, if indispensable as a matrix targeting signal, could be replaced by an internal sequence or a particular folding for recognition by the import machinery.

5-Aminolevulinate Synthetase↗
PubMed2000

3-acetylaltholactone and related styryl-lactones, mitochondrial respiratory chain inhibitors.

A novel furano-pyrone, 3-acetylaltholactone, and two other known styryl-lactones, altholactone and 5-acetoxyisogoniothalamin oxide, have been isolated from Goniothalamus arvensis (Annonaceae) stem bark. We report here the isolation and structural elucidation of these compounds with furane-pyrone and styryl-pyrone skeletons, postulating also for the first time their mechanism of cytotoxicity based on inhibition on mammalian mitochondrial respiratory chain.

Animals↗
PubMed1984

Transport of proteins into mitochondria.

There is still much that is obscure concerning the transport of proteins into or through the mitochondrial membrane systems. In addition, as pointed out previously, it is unlikely that the details of the process are the same for proteins destined for different compartments of the organelle. A brief summary of the process for matrix proteins might be as follows: The proteins are synthesized on free polysomes as precursors of higher molecular weight than the native forms. These precursors are liberated into the cell cytosol and subsequently translocated into the mitochondria. This timing might be different in yeast under some circumstances, synthesis being completed in association with the mitochondria. The precursors interact with a receptor in the outer mitochondrial membrane interaction being mediated by the presequences of the precursors. The presequences therefore act as addressing signals as well as possibly playing a role in one or all of (a) solubilization of precursors, (b) prevention of premature assembly into multimeric structures, or (c) maintenance of nonnative configurations required for transport. Interaction occurs with a second receptor, this time in the inner membrane of the mitochondria, interaction being with multiple sites in the polypeptide chain. Transport across the inner membrane then occurs, this transport depending on a transmembrane electrochemical gradient of which the proton component is the essential part. Transport is accompanied or followed by proteolysis of the prepiece, and formation of the native structure. While steps 1 and 2 of this sequence can be considered well established, the remaining steps are still poorly understood or purely hypothetical. Nevertheless, this sequence of events is consistent with known facts about the process and provides a framework for future investigations.

Animals↗
PubMed2002

Mitochondrial superoxide anion production and release into intermembrane space.

The topological distribution of ubiquinone in the mitochondrial respiratory chain suggests that both ubiquinone pools may participate in O2.- production and, hence, are vectorially released into the matrix and intermembrane space. Mitoplasts, obtained by either digitonin or hypotonic KCl treatment, are a suitable experimental model for measuring O2.- in the intermembrane space. The use of membrane-impermeable spin-broadening agents strengthens the notion that part of the O2.- generated by the respiratory chain may be released into the intermembrane space. This, together with the putative occurrence of a Cu, Zn-superoxide dismutase in this compartment may account for part of H2O2 released by mitochondria and contributing to a cytosolic steady-state level of this species in cytosol.

Animals↗