Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “inner membrane complex”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2Linked to original sources
PubMed1978

Nuclear surface complex as observed with the high resolution scanning electron microscope. Visualization of the membrane surfaces of the neclear envelope and the nuclear cortex from Xenopus laevis oocytes.

The nuclear envelope and associated structures from Xenopus laevis oocytes (stage VI) have been examined with the high resolution scanning electron microscope (SEM). The features of the inner and outer surfaces of the nuclear surface complex were revealed by manual isolation , whereas the membranes facing the perinuclear space (the space between the inner and outer nuclear membranes) were observed by fracturing the nuclear envelope in this plane and splaying the corresponding regions apart. Pore complexes were observed on all four membrane surfaces of this double-membraned structure. The densely packed pore complexes (55/micron2) are often clustered into triplets with shared walls (outer diameter = 90 nm; inner diameter = 25 nm; wall thickness = aproximately 30 nm), and project aproximately 20 nm above each membrane except where they are flush with the innermost surface. The pore complex appears to be an aggregate of four 30-nm subunits. The nuclear cortex, a fibrous layer (300 nm thickness) associated with the inner surface of the nuclear envelope, has been revealed by rapid fixation. This cortical layer is interrupted by funnel-shaped intranuclear channels (120-640 nm diam) which narrow towards the pore complexes. Chains of particles, arranged in spirals, are inserted into these intranuclear channels. The fibers associated with the innermost face of the nuclear envelope can be extraced with 0.6 MKI to reveal the pore complexes. A model of the nuclear surface complex, compiled from the visualization of all the membrane faces and the nuclear cortex, demonstrates relations between the intranuclear channels (3.2/micron2) and the numerous pore complexes, and the possibility of their role in nucleocytoplasmic interactions.

Animals↗
PubMed1975

Iron-sulfur components of succinate dehydrogenase: stoichiometry and kinetic behavior in activated preparations.

Extensively or completely activated preparations of beef heart succinate dehydrogenase have been investigated by electron paramagnetic resonance (EPR) techniques at 6 to 97 K. Reductive titrations with dithionite and rapid kinetic studies were performed with various types of soluble and membrane-bound preparations of the enzyme. The following components were detected and their behavior analyzed: a free radical, presumably arising from the covalently bound flavin on reduction, two iron-sulfur centers of the ferredoxin type, the signals of which appear on reduction, and a highpotential iron-sulfur component, detectable in the oxidized state. The high-potential component was only detected in complex II and inner-membrane preparations. This component and one of the ferredoxin-type centers were present in amounts close to stoichiometric with the flavin and were reduced by substrate. The other ferredoxin-type center was present in amounts between 0.1 and 0.5 times that of the flavin and was reduced only by dithionite. Of the components reduced by succinate, however, only a fraction (up to 50% of the high-potential iron-sulfur center and 40-60% of the ferredoxin-type iron-sulfur center) was reduced within the turnover time of the enzymes; In complex II not more than about 10% of the flavin appeared in the semiquinone form at any time. Soluble, purified preparations behaved similarly except that the high-potential component was nearly or completely absent and extensive accumulation of the free radical occurred (up to 70 to 80% of the flavin) in titration and kinetic experiments. No significant difference was observed between the rates of semiquinone formation and the reduction of the ferredoxin-type or high-potential centers by the substrate. Also no qualitative differences in the properties studied in this work became apparent between prepatations containing 4 or 8 iron atoms, respectively.

Animals↗
PubMed1975

Functional relationship between the ADP/ATP-carrier and the F1-ATPase in mitochondria.

1. The distribution of labeled and unlabeled adenine-nucleotides inside and outside mitochondria was followed after addition of [14C]ADP to rat liver mitochondria. Two types of mitochondria were used: 1, respiring mitochondria which were carrying out oxidative phosphorylation and which had been replenished in ATP by incubation in a medium supplemented with succinate and phosphate; 2, non-respiring mitochondria which had been partially depleted of ATP by incubation in a medium supplemented with rotenone and phosphate. During the first minute following addition of [14C]ADP to the respiring mitochondria, the pre-existing intramitochondrial (internal) [12C]ATP was released into the medium and replaced by newly synthesized [14C]ATP. No [14C]ADP accumulated in the mitochondria. It is suggested that extramitochondrial (external) ADP entering respiring mitochondria in exchange for internal ATP is phosphorylated to ATP before its complete release in the matrix space. In non-respiring mitochondria, the entry of [14C]ADP into the mitochondria was accompanied by the appearance in the external space of [12C]ADP and [12C]ATP, with a marked predominance of [12C]ADP. Thus in non-respiring mitochondria, the residual internal ATP is dephosphorylated to ADP in the inner membrane before being released outside the mitochondria. 2. When mitochondria were incubated with glutamate, ADP and [32P]phosphate, the [32P]ATP which accumulated in the matrix space became rapidly labeled in both the P gamma and P beta groups of the ATP, due to the presence of a transphosphorylation system in the mitochondrial matrix. The [32P]ATP which accumulated outside the mitochondria was also labeled in the P beta group, although less rapidly than the internal ATP. Our data show that a large fraction (75-80%) of the ATP produced by phosphorylation of added ADP within the inner mitochondrial membrane is released into the matrix space before being transported out from the mitochondria; only a small part (20-25%) is released directly outside the mitochondria without penetrating the matrix space. 3. In respiring and phosphorylating mitochondria, the value of the Km of the ADP-carrier for external ADP was 2-4 times lower than its value in non-respiring and non-phosphorylating mitochondria. 4. The above experimental data are discussed with reference to the topological and functional relationships between the ADP-carrier and the oxidative phosphorylation complex in the inner mitochondrial membrane. They strongly suggest that the ADP-carrier comes to the close neighbourhood of the ATP synthetase on the matrix side of the inner membrane.

Adenosine Diphosphate↗
PubMed1979

Topological studies of cytochromes P-450scc and P-45011 beta in bovine adrenocortical inner mitochondrial membranes. Effects of controlled tryptic digestion.

The topology of the steroid hydroxylase complexes in bovine adrenocortical mitochondria were studied by using controlled digestion with trypsin of purified inner mitochondrial membranes. Inhibition of steroid hydroxylase activity by trypsin was only observed in inner mitochondrial membranes which had been disrupted by various techniques. The steroid hydroxylase activity of intact inner membranes was not inhibited by trypsin. The effect of tryptic digestion was monitored by measuring 11 beta-hydroxylase and cholesterol side chain cleavage activities, as well as cytochrome P-450 reduction. The effect of trypsin on the steroid-induced difference spectra using pregnenolone, 20 alpha-hydroxycholesterol, and deoxycorticosterone was also measured. The results were similar regardless of which procedure was utilized and strongly suggest that both cytochrome P-45011 beta and cytochrome P-450scc are located on the matrix side of the mitochondrial inner membrane.

Adrenal Cortex↗
PubMedDate not supplied

[Isolation and characteristics of DNA fragments bound to mitochondrial membrane proteins].

Fragments of rat liver mitochondrial DNA were isolated. In vivo these fragments were able to form the complexes with the proteins of inner mitochondrial membrane. The fragments represent unique DNA regions with the secondary structure, their A-T content being equal to 82%. With the aid of phosphomonoesterase, polynucleotidkinase and gamma-(32P)-ATP mtDNA fragments were labeled and analyzed for oligopyrimidine composition. It was shown that they were enriched in di- and tri-oligo-pyrimidine blocks. The fragments are shown to form in vitro a complex with the membrane proteins. A single protein m. wt. 40,000) was reisolated from the complex.

Animals↗
PubMed1978

Paracrystalline arrays of membrane-to-membrane cross bridges associated with the inner surface of plasma membrane.

In cultured cells of the rat kangaroo PtK2 line, veils of the cell surface were observed which consisted of only plasma membrane and paracrystalline arrays of membrane-associated particles sandwiched in between. These membrane-to-membrane cross-bridging 9-to 11-nm wide particles were somewhat coumellar-shaped and were arranged on a hexagonal lattice with an interparticle distance of 16nm. At higher magnification, they revealed an unstained core, thus suggesting a ringlike substructure. Similar arrays of paracrystal-containing veils, which were rather variable in size and frequency, were also observed in other cultured cells. It is hypothesized that these paracrystals represent protein macromolecular complexes associated with the inner plasma membrane surface which crystallize when plasma membranes come into close intracellular contact and other components of the subsurface network are removed.

Animals↗
PubMed1978

Rat liver nuclear skeleton and ribonucleoprotein complexes containing HnRNA.

Rat liver nuclei deprived of chromatin and nucleoplasm show a spongelike network which preserves its connection with nucleoli, the inner membrane of the nuclear envelope, and nuclear pore complexes. It contains all of the HnRNA, provided the endogenous proteolytic activity is inhibited by a proteolytic inhibitor such as phenylmethyl sulfonyl chloride (PMSC) or the fluoride form (PMSF). In the absence of these proteolytic inhibitors, HnRNA is dissociated from the spongelike network and sediments in a sucrose gradient as polydispersed ribonucleoprotein complexes. Furthermore, purified HnRNA as well as rRNA do not bind to the spongelike network when added to these nuclei. These observations demonstrate that the association of HnRNA to the nuclear skeleton is not an artifact. RNase treatment of the spongelike network digests the majority of the rapidly labeled RNA but does not alter the morphological aspect nor the architecture of this network. EDTA and heparin treatments affect neither the attachment of HnRNA nor the structural organization of this network. Electron microscope studies of the network reveal a characteristic flexuous configuration. Its relationship with diffused and condensed chromatin is discussed.

Animals↗
PubMed1975

Studies on energy-linked reactions: isolation, characterisation and genetic analysis of trialkyl-tin-resistant mutants of Saccharomyces cerevisiae.

Mutants of Saccharomyces cerevisiae resistant to triethyl tin sulphate have been isolated and are cross-resistant to other trialkyl tin salts. Triethyl-tin-resistant mutants fall into two general phenotypic classes: class 1 and class 2. Class 1 mutants are cross-resistant to a variety of inhibitors and uncoupling agents which affect mitochondrial membranes (oligomycin, ossamycin, valinomycin, antimycin, erythromycin, chloramphenicol, '1799', tetrachlorotrifluoromethyl benzimidazole carbonylcyanide-m-chlorophenylhydrazone and cycloheximide). Class 2 mutants are specifically resistant to trithyl tin and the uncoupling agent "1799' [bis-(hexafluoroacetonyl)-acetone]. Triethyl tin at neutral pH values is a specific inhibitor of mitochondrial energy conservation reactions and prevents growth on oxidisable substrates such as glycerol and ethanol. Triethyl-tin-resistant mutants grow normally on glucose and ethanol in the presence of triethyl tin (10 muM). Biochemical studies indicate that the mutation involves a modification of the triethyl tin binding site on the mitochondrial inner membrane, probably the ATP-synthetase complex. Triethyl tin resistance/sensitivity in yeast is determined by cytoplasmic (mitochondrial) and nuclear genes. The mutants fall into a nuclear and a cytoplasmic (mitochondrial) class corresponding to the phenotypic cross-resistance classes 1 and 2. In the cytoplasmic mutants the triethyl tin resistance segregates mitotically and the resistance determinat is deleted by the action of ethidium bromide during petite induction. Recombination studies indicate that the triethyl tin mutations are not allelic with the other mitochondrial mutations at the loci RI, RIII and OLI. This indicates that the binding or inhibitory sites of oligomycin and triethyl tin are not identical and that the triethyl tin binding site is located on a different mitochondrial gene product to those which are involved in oligomycin binding. Interaction and cooperative effects between different binding sites on the mitochondrial inner membrane have been demonstrated in studies of the effect of the insertion of the TETr phenotype into mitochondrial oligomycin-resistant mutants and provide an experimental basis for complementation studies at the ATP-synthetase level.

Adenosine Triphosphatases↗
PubMed1978

The preparation and ultrastructure of avian erythrocyte nuclear envelope enclosed by the plasma membrane.

A procedure is described for the preparation of avian erythrocyte nuclear envelope ghosts which remain enclosed by the ellipsoid plasma membrane. Haemoglobin-free nucleated chicken erythrocyte ghosts are treated in a low ionic strength buffer plus heparin which brings about decondensation of the chromatin. This is followed by solubilization of the chromatin by digestion with pancreatic deoxyribonuclease-1. When studied by light microscopy using either phase-contrast or Nomarski interference optics, the ellipsoid plasma membrane is clearly seen to remain with the collapsed nuclear envelope trapped inside. This interpretation is supported by negative-staining electron microscopy using ammonium molybdate, which in addition reveals the presence of the nuclear pore complexes. The suggestion is advanced that structural protection is provided for the fragile nuclear envelope system by the surrounding plasma membrane, which might account for the final nuclear envelope being in the form of relatively intact ghosts with well defined nuclear pore complexes. The nuclear envelope is highly fragmented when the plasma membrane is absent, the nuclear pore complexes showing appreciable breakdown. Thin sectioning supports the results of negative staining and in addition shows the nuclear envelope retained within the plasma membrane to be composed of both inner and outer nuclear membranes, but the nuclear pore complexes are not clearly defined.

Animals↗
PubMed1979

Dopamine receptor sites in the anterior pituitary.

An immunocytochemical method was developed to visualize dopamine receptor sites on dispersed anterior pituitary cells of the rat. Dopamine receptors were labeled with the antagonist haloperidol. Some cells were incubated with haloperidol and a 100-fold excess of the potent antagonist D-butaclamol to determine nonspecific binding. The labeled sites were stained with an antibody against haloperidol and the peroxidase anti-peroxidase (PAP) technique. PAP complexes which served as markers for dopamine binding sites appeared on the outer plasmalemmal surface of the vast majority of mammotrophs. PAP complexes attached to the inner surface of endocytotic vesicle membrane suggested internalization of receptor-rich portions of the plasmalemma. Some gonadotrophs and somatotrophs were specifically stained to a lesser extent. However, high receptor site density and internalization of PAP complexes were never observed on cell types other than mammotrophs. The presence of dopamine receptors on the plasmalemma of mammotrophs provides strong additional evidence that dopamine acts upon these cells as a prolactin inhibitory hormone.

Animals↗
PubMed1977

Effect of an anti-tumor platinum complex, Pt(II) diaminotoluene, on mitochondrial membrane properties.

The effects of platinum complexes, selected for their potent anti-tumor activities, have been studied on rat liver mitochondria. Among the mitochondrial properties which have been studied, the most marked effects of platinum complexes were obtained on functions linked to the inner membrane. cis-Pt(II)(3,4-diaminotoluene) dichloride is shown to stimulate state 4 respiration. It inhibits the phosphate transport into mitochondria, decreases the accumulation of Ca2+, and induces a more rapid release of the accumulated Ca2+. A release of Mg2+ from mitochondria incubated in the absence of added divalent cations, and an efflux of divalent cations from mitochondrial membranes are also observed. All these results indicate a profound modification of the of the permeability of mitochondrial membrane.

Animals↗
PubMed1975

Septate-like junctions in abnormal erythroblasts: cytochemical, ultrastructural and freeze-etch studies.

Ultrastructural studies of the bone marrow of a patient with refractory anemia revealed aberrant erythroblasts with unique cell junctions. Periodic structures linked adjacent processes on the same cell as well as surfaces of neighboring erythroblasts. Inclusions circumscribed by similar complexes were also present in the cytoplasm. The junction appeared in cross sections as two rigidly parallel unit membranes separated by 250-300 A interspace with two regular arrays of facing 70 A particles at intervals of 160-200 A. These intracellular specializations were present between erythroblasts at various stages of maturation and between, mono, bi or multinucleated erythroblasts. Junctions were permeable to lanthanum and many that appeared to be intracellular were demonstrated to be continuous with the extracellular space. The fact that others were not penetrated by lanthanum indicates that detachment of the interdigitating processes from cells of origin could have occurred. In freeze-etched replicas, distribution of membrane particles was random in areas of septate-like junctions, although parallel rows were sometimes observed both on A and B inner hydrophobic faces of the membrane leaflets. Junctional complexes in tissue culture appeared to have been disrupted and were not reestablished; however, inclusions resembling internalized junctions were observed associated with multivesicular bodies. Ineffective erythropoiesis and the resulting refractory anemia appear to be associated with the presence of the described anomalous junctional complexes.

Anemia, Aplastic↗
PubMed1976

Assembly of ATPase protein in sarcoplasmic reticulum membranes.

Three specimen preparation techniques for electron microscopy were used to investigate the incorporation of the ATPase polypeptide chains in the membranes of fragmented sarcoplasmic reticulum (SR) obtained from rabbit skeletal muscle. Observations were made of both normal vesicles and vesicles exposed to trypsin, which is known to cleave the ATPase protein and to alter the ultrastructure of the vesicles in predictable ways. Freeze-fracture replicas reveal the typical 90-A particles on the concave (PF) faces with a density of 5,730 +/- 520/mum2. On the other hand both negatively stained and deeply etched preparations display outer projections, which are absent on trypsin-incubated vesicles. The etched specimens afford for the first time top views of the vesicles in the absence of any stain. These views reveal outer projections on the PS surface with a density of 21,000 +/- 3,900/mum2, a value nearly approximating the density of the ATPase polypeptide chains (106,000 mol wt) calculated on the basis of protein and membrane area determinations. On the other hand, this value is three to four times higher than that found for the density of the 90-A particles on the concave fracture faces. Since both outer projections and 90-A particles are identified with the ATPase protein, it is suggested that the ATPase polypeptide chains are amphiphilic molecules, with polar ends protruding individually as outer projections on the surface of the vesicles, and hydrophobic ends appearing as 90-A particles on the concave fracture faces. The discrepancy between the densities of the outer projections and the 90-A particles may be attributed either to variable penetration of the polypeptide chains into the membrane bilayer, or to formation of oligomers containing three or four hydrophobic ends and appearing as single 90-A particles. Each ATPase chain forms a complex with 20-30 phospholipid molecules. The remaining phospholipids (approximately 70% of the total SR phospholipids) account for less than half the membrane volume. It is proposed that the outer leaflet of the SR membrane is prevalently composed of the ATPase lipoprotein complex, and the inner leaflet is mostly a phospholipid monolayer.

Adenosine Triphosphatases↗
PubMed1978

Immunochemical analysis of inner and outer membranes of Escherichia coli by crossed immunoelectrophoresis.

Isolated membrane fractions of Escherichia coli K-12 yielded complex immunoprecipitate patterns when Triton X-100 and sodium dodecyl sulfate extracts were examined by crossed immunoelectrophoresis with antienvelope immunoglobulins. Twelve of the 46 antigens in the immunoprecipitate patterns of inner (plasma) membranes were identified by zymograms and/or by the use of specific antisera. The following enzyme activities were detected in immunoprecipitates: 6-phosphogluconate dehydrogenase (EC 1.1.1.43); adenosine triphosphatase (EC 3.6.1.3); glutamate dehydrogenase (EC 1.4.1.4), two separate components; malate dehydrogenase (EC 1.1.1.37); dihydroorotate dehydrogenase (EC 1.3.3.1); succinate dehydrogenase (EC 1.3.99.1); lactate dehydrogeanse (EC 1.1.1.27); reduced nicotinamide adenine dinucleotide dehydrogenase (EC 1.6.99.3); protease (EC 3.4.21.1); and glycerol 3-phosphate dehydrogenase (EC 1.1.99.5). The corresponding immunoprecipitate pattern for isolated outer membranes consisted of at least 25 discrete antigens and differed strikingly from that obtained with inner membranes. Two major immunogens were identified as lipopolysaccharide and Braun lipoprotein. A protease-active immunoprecipitate was also detected in this fraction, but attempts to identify the Rosenbusch matrix protein in the crossed immunoelectrophoretic profile were unsuccessful.

Antigens, Bacterial↗
PubMed1977

Effect of membrane environment on succinate dehydrogenase activity.

The turnover number of succinate dehydrogenase from mammalian heart determined by the spectrophotometric phenazine methosulfate assay, after complete activation, is approximately 21,000 mol of succinate oxidized/min/mol of histidyl flavin at 38 degrees in relatively intact inner membrane preparations and mitochondria. Reconstitutively active soluble preparations, extracted anaerobically in the presence of succinate from inner membrane preparations show turnover numbers of 11,500 to 14,500 and a significantly lower apparent Km for phenazine methosulfate than the parent particles. The decline of both the turnover number and of the Km occurs during the brief period when the enzyme is detached from the membrane. The observed values represent the activities in the soluble extract of both the reconstitutively active and reconstitutively inactive enzyme. The latter may be from 10 to 40% even in the most carefully prepared enzyme; it has a lower turnover number in the phenazine methosulfate assay than the average for the solution and is devoid of catalytic activity in the "low Km" ferricyanide assay (Vinogradov, A. D., Ackrell, B.A.C., and Singer, T.P. (1975) Biochem. Biophys. Res. Commun. 67, 803-809). The reconstitutively active form of the soluble enzyme has a turnover number of at least 15,000 and an equal activity in the low Km ferricyamide assay. When recombined with the membrane the total activity of the enzyme is increased by over 60% and it regains the original turnover number, Km for phenazine methosulfate, and sensitivity of the phenazine methosulfate reductase activity to thenoyltrifluoroacetone, carboxamides, and cyanide. It appears, therefore, that the membrane environment or some component of it exerts a positive modulating influence on the enzyme even in the fully activated state. In certain particulate sources (Keilin-Hartree preparations, Complex II) the enzyme shows lower turnover numbers (11,000 to 12,500) than in more intact inner membranes. This seems to be due to inactivation in the course of preparation and, in the case of Complex II, in part also to loss of the normal membrane environment or of a membrane component, possibly Q-10, during isolation.

Animals↗
PubMed1978

Immunocytochemical localization of the major polypeptides of the nuclear pore complex-lamina fraction. Interphase and mitotic distribution.

This laboratory has previously isolated a fraction from rat liver nuclei consisting of nuclear pore complexes associated with the proteinaceous lamina which underlies the inner nuclear membrane. Using protein eluted from sodium dodecyl sulfate (SDS) gels, we have prepared antibodies in chickens to each of the three predominant pore complex-lamina bands. Ouchterlony double diffusion analysis shows that each of these individual bands cross-reacts strongly with all three antisera. In immunofluorescence localization performed on tissue culture cells with these antibodies, we obtain a pattern of intense staining at the periphery of the interphase nucleus, with little or no cytoplasmic reaction. Electron microscope immunoperoxidase staining of rat liver nuclei with these antibodies labels exclusively the nuclear periphery. Furthermore, reaction occurs in areas which contain the lamina, but not at the pore complexes. While our isolation procedure extracts the internal contents of nuclei completely, semiquantitative Ouchterlony analysis shows that it releases negligible amounts of these lamina antigens. Considered together, our results indicate that these three bands represent major components of a peripheral nuclear lamina, and are not structural elements of an internal "nuclear protein matrix." Fluorescence microscopy shows that the perinuclear interphase localization of these lamina proteins undergoes dramatic changes during mitosis. Concomitant with nuclear envelope disassembly in prophase, these antigens assume a diffuse localization throughout the cell. This distribution persists until telophase, when the antigens become progressively and completely localized at the surface of the daughter chromosome masses. We propose that the lamina is a biological polymer which can undergo reversible disassembly during mitosis.

Cell Cycle↗