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PubMed1997

Calcium site specificity. Early Ca2+-related tight junction events.

The molecular mechanisms by which Ca2+ and metal ions interact with the binding sites that modulate the tight junctions (TJs) have not been fully described. Metal ions were used as probes of these sites in the frog urinary bladder. Basolateral Ca2+ withdrawal induces the opening of the TJs, a process that is abruptly terminated when Ca2+ is readmitted, and is followed by a complete recovery of the TJ seal. Mg2+ and Ba2+ were incapable of keeping the TJ sealed or of inducing TJ recovery. In addition, Mg2+ causes a reversible concentration-dependent inhibition of the Ca2+-induced TJ recovery. The effects of extracellular Ca2+ manipulation on the TJs apparently is not mediated by changes of cytosolic Ca2+ concentration. The transition elements, Mn2+ and Cd2+, act as Ca2+ agonists. In the absence of Ca2+, they prevent TJ opening and almost immediately halt the process of TJ opening caused by Ca2+ withdrawal. In addition, Mn2+ promotes an almost complete recovery of the TJ seal. Cd2+, in spite of stabilizing the TJs in the closed state and halting TJ opening, does not promote TJ recovery, an effect that apparently results from a superimposed toxic effect that is markedly attenuated by the presence of Ca2+. The interruption of TJ opening caused by Ca2+, Cd2+, or Mn2+, and the stability they confer to the closed TJs, might result from the interaction of these ions with E-cadherin. Addition of La3+ (2 microM) to the basolateral Ca2+-containing solution causes an increase of TJ permeability that fully reverses when La3+ is removed. This effect of La3+, observed in the presence of Ca2+ (1 mM), indicates a high La3+ affinity for the Ca2+-binding sites. This ability of La3+ to open TJs in the presence of Ca2+ is a relevant aspect that must be considered when using La3+ in the evaluation of TJ permeability of epithelial and endothelial membranes, particularly when used during in vivo perfusion or in the absence of fixatives.

Animals↗

PubMed2000

Golgi apparatus immunolocalization of endomannosidase suggests post-endoplasmic reticulum glucose trimming: implications for quality control.

Trimming of N-linked oligosaccharides by endoplasmic reticulum (ER) glucosidase II is implicated in quality control of protein folding. An alternate glucosidase II-independent deglucosylation pathway exists, in which endo-alpha-mannosidase cleaves internally the glucose-substituted mannose residue of oligosaccharides. By immunogold labeling, we detected most endomannosidase in cis/medial Golgi cisternae (83.8% of immunogold labeling) and less in the intermediate compartment (15.1%), but none in the trans-Golgi apparatus and ER, including its transitional elements. This dual localization became more pronounced under 15 degrees C conditions indicative of two endomannosidase locations. Under experimental conditions when the intermediate compartment marker p58 was retained in peripheral sites, endomannosidase was redistributed to the Golgi apparatus. Double immunogold labeling established a mutually exclusive distribution of endomannosidase and glucosidase II, whereas calreticulin was observed in endomannosidase-reactive sites (17.3% in intermediate compartment, 5.7% in Golgi apparatus) in addition to the ER (77%). Our results demonstrate that glucose trimming of N-linked oligosaccharides is not limited to the ER and that protein deglucosylation by endomannosidase in the Golgi apparatus and intermediate compartment additionally ensures that processing to mature oligosaccharides can continue. Thus, endomannosidase localization suggests that a quality control of N-glycosylation exists in the Golgi apparatus.

Animals↗

PubMed2002

Molybdoenzymes and molybdenum cofactor in plants.

The transition element molybdenum (Mo) is essential for (nearly) all organisms and occurs in more than 40 enzymes catalysing diverse redox reactions, however, only four of them have been found in plants. (1) Nitrate reductase catalyses the key step in inorganic nitrogen assimilation, (2) aldehyde oxidase(s) have been shown to catalyse the last step in the biosynthesis of the phytohormone abscisic acid, (3) xanthine dehydrogenase is involved in purine catabolism and stress reactions, and (4) sulphite oxidase is probably involved in detoxifying excess sulphite. Among Mo-enzymes, the alignment of amino acid sequences permits domains that are well conserved to be defined. With the exception of bacterial nitrogenase, Mo-enzymes share a similar pterin compound at their catalytic sites, the molybdenum cofactor. Mo itself seems to be biologically inactive unless it is complexed by the cofactor. This molybdenum cofactor combines with diverse apoproteins where it is responsible for the correct anchoring and positioning of the Mo-centre within the holo-enzyme so that the Mo-centre can interact with other components of the enzyme's electron transport chain. A model for the three-step biosynthesis of Moco involving the complex interaction of six proteins will be described. A putative Moco-storage protein distributing Moco to the apoproteins of Mo-enzymes will be discussed. After insertion, xanthine dehydrogenase and aldehyde oxidase, but not nitrate reductase and sulphite oxidase, require the addition of a terminal sulphur ligand to their Mo-site, which is catalysed by the sulphur transferase ABA3.

Abscisic Acid↗

PubMedDate not supplied

Studies of tissue NMR relaxation enhancement by manganese. Dose and time dependences.

Manganese is a powerful paramagnetic material and potential NMR contrast agent. It drastically affects the NMR properties of solutions and tissues and is less toxic than most other transition elements. It also possesses some unusual and advantageous features; it alters T1 and T2 to different degrees, and it can bind to macromolecules to become even more effective at reducing proton relaxation times. The dose dependence of tissue relaxation rate increases has been measured in mice, and proton relaxation enhancement ratios that describe binding effects have been evaluated. These ratios imply that a tenfold reduction in manganese dose is achievable when the ion binds to intracellular components, and it is demonstrated that such binding effects can be a major factor in the efficacy of contrast enhancement. The effect of manganese on the ratio T1/T2 is dose dependent so that lower doses may be more useful for some imaging techniques. The postmortem time course of relaxation times in organs containing manganese varies between organs and with manganese content, and demonstrates that the relationship between tissue relaxation enhancement and metal content is not a simple correlation with concentration since large variations in T1 and T2 can occur even when metal and water content are fixed.

Animals↗

PubMed1986

The reorganization of the Golgi complex in anoxic pancreatic acinar cells.

An extensive reorganization of the Golgi complex (GC) was found in the acinar cells of pancreatic lobules incubated in vitro under conditions which inhibited ATP synthesis and thereby blocked the intracellular transport of secretory proteins. After 15-min incubation under N2 or in the presence of 1 mM dinitrophenol (DNP), transitional elements of the endoplasmic reticulum (ER) lost their protrusions, small peripheral Golgi vesicles decreased drastically in number, and fibrillar aggregates approximately 0.2 to 0.5 micron in diameter appeared on the cis side of the stacks of Golgi cisternae. These aggregates often contained vesicle-free, small (approximately 40 nm), globular cages and, occasionally, vesicle-free, clathrin-like cages. Fibrillar aggregates were also observed on the trans side of Golgi stacks. Other changes included the proliferation of GERL-elements ("rigid lamellae") and a striking increase in the population of coated vesicles trans to the Golgi complex and throughout the apical region of the anoxic acinar cells. All changes were found to be reversible provided the cells were incubated for less than 1 h under N2. These observations suggest that the fibrillar elements and the associated cages described in this study may play a role in the vesicular transport of newly synthesized proteins from the ER to the Golgi complex. Further work is needed to explore this possibility.

Animals↗

PubMed1979

Symbionticism revisited: a discussion of the evolutionary impact of intracellular symbioses.

Wallin (1927) first published the notion that the fusion of bacteria with host cells was the principal source of genetic novelty for speciation. He suggested that mitochondria are transitional elements in this process. While the significance that he attributed to symbiosis now seem excessive, he was one of the first authors to be aware of the evolutionary potential of symbiotic events and his view of mitochondria may not seem strange to many cell biologist today. The most significant evolutionary development which has been attributed to intracellular symbiosis is the origin of eukaryotic cellular organization. The current status of the 'serial endosymbiosis hypothesis' is briefly review. The case for the symbiotic origin of the chloroplast, based principally on 16 S RNA oligonucleotide cataloguing, is very strong. Mitochondrial origins are more obscure but also appear to be symbiotic due to recent 18 S cataloguing from wheat embryos. The probablility of the multiple origin of some eukaryotic organelles is also examined, the processes in question being the acquisition of distinct stocks of chloroplasts from disparate photosynthetic prokaryotes and the secondary donation of organelles from degenerate eukaryotic endosymbionts to their hosts, with specific reference to the dinoflagellates Peridinium balticum, Kryptoperidinium foliaceum and the ciliate Mesodinium rubrum. It is concluded that the evolutionary potential of intracellular symbiosis ('cytobiosis': a term introduced in this paper) is great, with the best established influence being on the origin of eukaryotic chloroplasts. Together with the potential effects of viral vectors, symbiosis serves as a supplementary speciation mechanism capable of producing directed evolutionary changes. It is likely that these processes will explain some of the apparent anomalies in evolutionary rates and direction which are not readily explicable by the conventional synthetic theory of evolution.

Animals↗

PubMed2003

Tunneling as a stochastic process: a path-integral model for microwave experiments.

Delay time results obtained in microwave experiments at frequencies above and below the cutoff frequency of different waveguide sections are interpreted on the basis of wave propagation in the presence of dissipative effects. Kac's original suggestion was the starting point for the formulation of a stochastic model, which has now been substantially improved, also in relation to the transition-elements theory of Feynman-Hibbs. In this way, an approach to the problem is provided, which is completely distinct from the ones formulated elsewhere.

Journal Article↗

PubMed2003

Sum rules in x-ray resonant Raman scattering: recovering the Co ground state information in CoFe2O4 as a test case.

We present an approach to x-ray resonant Raman scattering suitable for sum-rule analysis. In magnetic systems it gives ground state information as represented by an expansion in coupled multipoles of orbital and spin moments. The experiment is based on the angular dependence of the integrated peak intensities. In 3d transition elements one obtains information up to order 4 from the channel 2p(6)3d(n)-->2p(5)3d(n+1)-->2p(6)3s(1)3d(n+1). By combining these results with L(2,3) absorption dichroism, we show quantitatively the atomiclike properties of cobalt in CoFe2O4 up to high-order multipoles.

Journal Article↗

PubMed2001

Tetrakis(mu-acetato-O,O')bis[(4-cyanopyridine-N)copper(II)].

The title compound, [Cu(2)(C(2)H(3)O(2))(4)(C(6)H(4)N(2))(2)], has the familiar lantern-type structure that is characteristic of dimetal tetracarboxylates of copper and several other transition elements. The molecule lies about an inversion centre and the Cu atom is present in a distorted square-pyramidal coordination environment, consisting of four O atoms in equatorial positions and the pyridyl-N atoms of the two 4-cyanopyridine ligands in axial positions.

Journal Article↗

PubMed1977

Organometallic and organometalloid compounds as standards for microprobe analysis of epoxy resin embedded tissue.

X-ray microanalysis of phosphorus, transition elements and heavy metals in biological tissue is frequently carried out on thin sections of specimens embedded in epoxy resin. A logical choice for the quantitive microprobe analysis of these specimens is a standard, consisting of a homogenous solution of the elements of interest in the epoxy resin. Four kinds of compounds were found suitable for this purpose: (1) phenyl compounds containing group Vb elements, (2) cyclopentadienyl-derivatives, (3) a pentanedione derivative (acetylacetonate) and (4) complexes of metals with dialkyldithiocarbamates. In the latter case, the standard also contains sulphur. Standards for P, Sb (1) Mn, Fe (2) Ni (3) Cu, Zn, Cd, Hg, Pb, Bi (4) were prepared in Epon 812 or Spurr epoxy resin. The compounds were mixed with the resin (without accelerator) to which some propylene oxide may be added, and dissolved immediately or after short heating. The maximal concentration of metal was in the order of magnitude of several promilles to 1%. Solubility in the Spurr resin was better than in Epon 812. After addition of the accelerator, polymerization was carried out as usual. The compounds used are commercially availalbe at low cost or can be easily prepared.

Alkanes↗

PubMed1981

Preferential inhibition of ribonucleic acid synthesis by a new thiosemicarbazone possessing antibacterial and antiparasitic properties.

We determined the influence of the azacycloheptane derivative (H) of a 2-acetylpyridine thiosemicarbazone on growth and macromolecular synthesis in Escherichia coli AT-9. Thiosemicarbazone H caused bacteriostasis and a primary inhibition of ribonucleic acid synthesis; secondary effects included inhibition of deoxyribonucleic acid and protein synthesis. Addition of cooper or other transition elements was not necessary for these inhibitions.

Anti-Bacterial Agents↗

PubMed1996

Growth phase-dependent transcription of the sigma(54)-dependent Po promoter controlling the Pseudomonas-derived (methyl)phenol dmp operon of pVI150.

Transcription from Pseudomonas-derived -24, -12 Po promoter of the pVI150-encoded dmp operon is mediated by the sigma 54-dependent DmpR activator in response to the presence of aromatic pathway substrates in the medium. However, global regulatory mechanisms are superimposed on this regulatory system so that the specific response to aromatic effectors is absent in cultures until the stationary phase is reached. Here we genetically dissect the system to show that the growth phase response is faithfully mimicked by a minimal system composed of the dmpR regulatory gene and the Po promoter regulatory region and can be reproduced in heterologous Escherichia coli. Using this system, we show that the growth phase-dependent DmpR-mediated response to aromatic compounds is limited to fast-growing cultures. Thus, during exponential growth of cultures in minimal media containing different carbon sources, the response to aromatics is immediate, while the response is suppressed in cultures grown on rich media until the exponential-to-stationary phase transition. Elements known to be involved in the DmpR-mediated transcription from Po were analyzed for the ability to influence the growth phase response. Most dramatically, overexpression of DmpR was shown to completely abolish the growth phase response, suggesting that a negatively acting factor may mediate this level of regulation. The possible mechanism of action and integration (of the specific regulation of the dmp operon-encoded catabolic enzymes with the physiological status of the bacteria are discussed.

Bacterial Proteins↗

PubMed1998

Okadaic acid induces selective arrest of protein transport in the rough endoplasmic reticulum and prevents export into COPII-coated structures.

Quantitative immunoelectron microscopy and subcellular fractionation established the site of endoplasmic reticulum (ER)-Golgi transport arrest induced by the phosphatase inhibitor okadaic acid (OA). OA induced the disappearance of transitional element tubules and accumulation of the anterograde-transported Chandipura (CHP) virus G protein only in the rough ER (RER) and not at more distal sites. The block was specific to the early part of the anterograde pathway, because CHP virus G protein that accumulated in the intermediate compartment (IC) at 15 degrees C could gain access to Golgi stack enzymes. OA also induced RER accumulation of the IC protein p53/p58 via an IC-RER recycling pathway which was resistant to OA and inhibited by the G protein activator aluminium fluoride. The role of COPII coats in OA transport block was investigated by using immunofluorescence and cell fractionation. In untreated cells the COPII coat protein sec 13p colocalized with p53/p58 in Golgi-IC structures of the juxtanuclear region and peripheral cytoplasm. During OA treatment, p53/p58 accumulated in the RER but was excluded from sec 13p-containing membrane structures. Taken together our data indicate that OA induces an early defect in RER export which acts to prevent entry into COPII-coated structures of the IC region.

Animals↗

PubMed1978

The response of cell walls of Bacillus subtilis to metals and to electron-microscopic stains.

Purified cell walls of Bacillus subtilis were subjected to solutions of 40 independent metals and the metal uptake, the electron-scattering power of thin sections, and the type of staining response evaluated. This was repeated for six typical electron-microscopic stains (uranyl acetate, uranyl magnesium acetate, osmium tetroxide, Os-meth, osmium-dimethylethylenediamine, and ruthenium red) and one new staining reagent (a potassium platinum chloride - dimethylsulfoxide complex) whose specificity is for amine functions. The reaction of select metals can be specific in terms of both uptake and staining response. Of the metals studied most transition elements had a high affinity for the wall fabric and some (i.e., Sc III, most lanthanides, UIV, ZrIV,HfIV, Fe III, Pd II, Ru III, and In III) may be suitable as contrasting agents for electron microscopy. Furthermore, when the thickness of metal-reacted walls was compared to freeze-each and ultracryotomy data, statistical-dimensional differences were commonly seen, which indicates that wall ultrastructure can be profoundly affected by the type of metal and (or) staining reagent.

Bacillus subtilis↗

PubMed1989

Meningiomas: MR and histopathologic features.

The magnetic resonance (MR) appearances of 40 biopsy-proved meningiomas were blindly evaluated and correlated with their predominant histologic pattern--fibroblastic, transitional, syncytial, angioblastic, or mixed. T1-weighted images were not particularly useful in discriminating pathologic subtype, because most tumors were isointense with or hypointense to cortex regardless of histologic type. Signal intensity and features on T2-weighted images strongly correlated with histopathologic findings in over 75% of cases, however. Meningiomas markedly hypointense to cortex on T2-weighted images (seven of 40 cases) were composed predominantly of fibroblastic or transitional elements, while markedly hyperintense meningiomas (14 of 40 cases) demonstrated predominance of syncytial or angioblastic elements. Consideration of secondary features visible at MR imaging (degree of edema, cyst formation, presence of calcium aggregates) led to a more specific histologic prediction in over half of the remaining isointense tumors. The varied MR appearance of meningiomas has a clear histologic basis, and crude prediction of pathologic subtype is possible in over three-fourths of cases.

Brain Neoplasms↗

PubMed1989

Immunocytochemical localization of BiP to the rough endoplasmic reticulum: evidence for protein sorting by selective retention.

Immunoglobulin heavy chain binding protein (BiP) (also known as GRP 78) is a protein of the endoplasmic reticulum (ER) which has been shown to be involved in post-translational processing of nascent membrane and secretory proteins. To determine BiP's location in the exocytic pathway, we localized BiP at the electron microscopic level in mouse myeloma cell lines by immunoperoxidase cytochemistry. BiP was found to be present within the cisternal spaces of the RER and nuclear envelope but was not detected in the cisternae of the Golgi complex. BiP reaction product was also found within transitional elements of the RER but was absent from smooth-surfaced vesicles found between the ER and the Golgi complex. Immunoperoxidase staining of BiP was reduced or absent in regions of a smooth ER membrane system in myelomas that contained endogenous murine retrovirus A particles. All compartments of the exocytic pathway, including the virus-containing smooth ER, stained for IgG, a secretory protein. These observations suggest that BiP is selectively retained in the cisternae of the ER and is not free to enter Golgi-directed transport vesicles. These studies suggest that BiP's subcellular localization may occur by selective interaction with component(s) of the ER.

Animals↗

PubMed1994

A possible role for stable microtubules in intracellular transport from the endoplasmic reticulum to the Golgi apparatus.

The intracellular transport of secretory proteins involves at an early stage the formation of vesicles from transitional elements of the endoplasmic reticulum (ER) containing these proteins and the transfer of these vesicles to the cis-face of the Golgi apparatus. We propose that the latter transfer process does not occur by random diffusion, but is instead mediated by tracking along stable microtubules. To test this proposal, we have carried out double immunoelectron microscopic labeling experiments on frozen sections of HepG2 hepatoma cells secreting the protein human serum albumin (HSA). By a cycloheximide treatment protocol, the stage during which the transfer of newly synthesized HSA from the ER to the Golgi apparatus occurs in vivo was determined. Sections of the cells were then double immunolabeled using primary antibodies to HSA and to glu-tubulin, the latter specifically detecting stable microtubules. We observed a significantly high frequency of HSA-containing structures between the ER and the Golgi apparatus with which stable microtubules were closely associated. These results support the proposal that stable microtubules may play a critical role in directing the transfer process from the ER to the Golgi apparatus.

Biological Transport, Active↗

PubMed2005

Concentration levels of major and trace elements in rice from Sri Lanka as determined by the k0 standardization method.

Instrumental neutron activation (INAA) with k0 standardization has been used to determine the concentration levels of a variety of major and trace elements (Al, As, Br, Cd, Cl, Co, Cr, Cs, Cu, Fe, Hg, K, La, Mg, Mn, Mo, Na, Rb, Sc, Se, and Zn) in rice grains (raw and parboiled) and in rice flour collected from local markets in Sri Lanka. In addition, the energy-dispersive X-ray fluorescence (EDXRF) analysis has been used to determine the three elements Ca, P, and S in powdered samples. To evaluate and assure the accuracy and precision of the k0 standardization method, the IAEA standard reference material V-8 rye flour was analyzed. The results obtained in the present investigation were compared with the results reported from other countries. All of the elements detected in the rice matrices from Sri Lanka were very low in concentration or within normal limits for food plants. Approximate daily dietary intakes of the individual elements supplied through rice were calculated and compared with the available literature values of daily allowances.

Calcium↗