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L L Chen

Publications and source records attributed to L L Chen.

At least 109 records · Page 6Linked to original sources
PubMed1988

Effect of ammonium nitrate on the heterocyst differentiation and nitrogen fixing activity of Anabaena HA 101.

Heterocysts were able to be induced while the blue-green alga Anabaena HA 101 were grown in a medium free from ammonium nitrate, but the heterocyst formation was inhibited while the Anabaena were grown in medium containing 5 mM ammonium nitrate. Heterocysts which had already formed were enhanced to senescence by the ammonium nitrate. Heterocyst transformation from certain vegetative cells into adult heterocysts accompanied with protein synthesis. A maximal level of protein synthesis as well as the high activity of nitrogenase was detected while the late proheterocysts transformed to mature heterocysts. Heterocyst is the site of nitrogenase synthesis and of the nitrogen fixation.

Culture Media↗
PubMed1986

Misread protein creates membrane channels: an essential step in the bactericidal action of aminoglycosides.

Among the pleiotropic effects of aminoglycosides, their irreversible uptake and their blockade of initiating ribosomes have appeared to explain their bactericidal action, while the contributions of translational misreading and membrane damage and the mechanism of that damage have remained uncertain. We now present evidence that incorporation of misread proteins into the membrane can account for the membrane damage. The bactericidal action thus appears to result from the following sequence, in which each step is essential: slight initial entry of the antibiotic; interaction with chain-elongating ribosomes, resulting in misreading; incorporation of misread protein into the membrane, creating abnormal channels; increased (and irreversible) entry through these channels, and hence increased misreading and formation of channels; and, finally, blockade of initiating ribosomes. This mechanism can account for several previously unexplained observations: that streptomycin uptake requires protein synthesis during, but not after, the lag before the membrane damage; that streptomycin-resistant cells, which fail to take up streptomycin, can do so after treatment by another aminoglycoside; and that puromycin at moderate concentrations accelerates streptomycin uptake, while high concentrations (which release shorter chains) prevent it. In addition, puromycin, prematurely releasing polypeptides of normal sequence, also evidently creates channels, since it is reported to promote streptomycin uptake even in streptomycin-resistant cells. These findings imply that normal membrane proteins must be selected not only for a hydrophobic anchoring surface, but also for a tight fit in the membrane.

Alkaline Phosphatase↗
PubMed1986

Roles of H+-ATPase and proton motive force in ATP-dependent protein translocation in vitro.

Membrane vesicles from an Escherichia coli mutant with a deletion of the uncBC operon required ATP to translocate proteins, thus ruling out an essential role of F1F0-H+-ATPase in ATP-dependent protein translocation. Moreover, proteins could be translocated in the absence of proton motive force. At suboptimal ATP concentrations, D-lactate stimulated protein translocation, indicating that proton motive force, although insufficient to support translocation, could facilitate the process.

Adenosine Triphosphate↗
PubMed1983

Enhanced acetylcholinesterase staining in the hippocampal perforant pathway zone after combined lesions of the septum and entorhinal cortex.

A lesion of the septum or a transection of the fimbria-fornix diminishes most, but not all, acetylcholinesterase (AChE) staining in the hippocampal formation. The residual AChE is located in the outer part of the molecular layer of the hippocampal CA1 zone and adjacent subicular field (zone 31). We report that following combined lesions of the septum and entorhinal cortex, the residual hippocampal AChE staining pattern expands and occupies the zone innervated normally by perforant pathway terminals from the entorhinal cortex.

Acetylcholinesterase↗
PubMed1978

Anatomy of germinal centers in mouse spleen, with special reference to "follicular dendritic cells".

Lymphocyte proliferation in germinal centers (GC's) is thought to be triggered by antigen retained extracellularly on the surface of special "dendritic" cells. The anatomy and function of these cells have not been studied directly or in detail. We therefore examined mouse spleen GC's developing in response to sheep erythrocyte stimulation. We found that distincitve "follicular dendritic cells" (FDC's) were present in both the GC and adjacent mantle region of secondary follicles. The large, irregularly shaped nucleus, containing little heterochromatin, allowed for the light microscope (LM) identification of FDC's. By EM, the cell was stellate in shape sending out long, thin sheets of cytoplasm which could fold and coil into complex arrays. The processes were coated extracellularly by an amorphous electron-dense material of varying thickness, as well as particulates including variable numbers of virions. The FDC cytoplasm lacked organelles of active secretory and endocytic cells, such as well-developed rough endoplasmic reticulum (RER) and lysosomes. These anatomical features readily distinguished FDC's from other cell types, even those that were extended in shape. To pursue these descriptive findings, we injected three electron-dense tracers i.v. and sacrificed the mice 1 h-10 days thereafter. Colloidal carbon, colloidal thorium dioxide (cThO2), and soluble horseradish peroxidase (HRP) were actively sequestered into the vacuolar system of macrophages but were interiorized only in trace amounts by FDC's. Therefore, FDC's are not macrophages by cytologic and functional criteria. FDC's did display a unique property. Both colloidal carbon and thorium dioxide, which are nonimmunogens, could be visualized extracellularly on the cell surface for several days. The meaning of this is unclear, but the association of colloid with FDC's appeared to slow the movement of particulates through the extracellular space into the GC proper. FDC's were not readily identified in splenic white pulp lacking GC's. They must develop de novo then, possibly from novel dendritic cells that we have identified in vitro (Steinman, R. M., and Z. A. Cohn. 1973. J. Exp. Med. 137:1142-1162).

Animals↗
PubMed1978

Distribution of horseradish peroxidase (HRP)-anti-HRP immune complexes in mouse spleen with special reference to follicular dendritic cells.

The distribution of immune complexes has been studied in mouse spleen stimulated to contain many germinal centers (GC's). Horseradish peroxidase (HRP)-anti-HRP complexes were used as an appropriately precise and sensitive model. We were primarily interested in the relative abilities of three cell types to interact with complexes: lymphocytes, macrophages, and follicular dendritic cells (FDC's). The latter are distinctive, nonendocytic, stellate cells located primarily at the transition of mantle and GC zones of 2 degrees lymphoid follicles (Chen, L. L., J. C. Adams, and R. M. Steinman, 1978, J. Cell Biol. 77:148). Binding of immune complexes to lymphocytes could not be visualized in situ. Macrophages avidly interiorized complexes into lysosomes, but did not retain them extracellularly. In contrast, FDC's could retain HRP-anti-HRP extracellularly under appropriate conditions, but did not endocytose them. Cytochemical reactivity accumulated progressively on FDC's 1--6 h after administration of complexes i.v., remained stable in amount and location for 1 day, and then was progressively lost over a 1- to 5-day period. Several variables in the association of complexes with macrophages and FDC's were pursued. Only 1 microgram of complexed HRP had to be administered to visualize binding to both cell types. Macrophages interiorized complexes formed in a wide range of HRP/anti-HRP ratios, while FDC's associated with complexes formed in HRP excess only. Quantitative studies with [125I]HRP-anti-HRP demonstrated that 20% of the splenic load of HRP associated with FDC's. Complexes formed with an F(ab')2 anti-HRP were distributed primarily in macrophages. When the levels of the third component of serum complement were depleted by prior treatment with cobra venom factor, uptake of complexes by macrophages was reduced some 50% whereas association with FDC's was abolished. The fact that antigen excess complexes are retained extracellularly strengthens the idea that they are immunogenic. Finally, the association of complexes with FDC's seems to retard the entry of antigen into the GC proper.

Animals↗
PubMed1977

Synthesis and secretion of albumin by a synchronized rat hepatoma cell line.

The rat hepatoma cell H4-12 which synthesizes and secretes albumin was synchronized by growth in isoleucine-deficient medium followed by a second block with excess thymidine. Albumin synthesis and secretion was measured in the synchronized cells at different time intervals representative of early S, late S, G2, mitosis, early G1 and late G1 phases of the cell cycle. Maximal albumin synthesis occurred during G1 although significant synthesis also occurred during the other cell cyle phases. Most (75--80%) of the radioactive albumin produced during a 15 min pulse incubation with L-[4,5-3H] leucine was found in the microsomal cell fraction and this nascent albumin was secreted into the incubation medium during a 160 min chase period. Fifty percent of the nascent albumin was secreted by 50--55 min and this pattern of secretion did not change during the cell cycle. These data indicate that albumin synthesis occurs throughout the cell cycle but that it is preferred during G1. The rate of intracellular transport and secretion of albumin does not vary during the different phase of the cell cycle.

Albumins↗
PubMed1976

The flagellar membrane of Ochromonas danica. Isolation and electrophoretic analysis of the flagellar membrane, axonemes, and mastigonemes.

The isolation and purification of the flagellar membrane of the phytoflagellate, Ochromonas danica, is described. The procedure is simple, mild, rapid, and it produces a pure membrane preparation. The method additionally permits the isolation of clean preparations of axonemes and mastigonemes from a single flagella preparation. Each component was studied by electron microscopy and acrylamide gel electrophroesis. The isolated flagella preparation was nearly free of other cellular organelles as judged by phase contrast and electron microscopy. The purified membrane preparation consisted of small vesicles (500 to 1500 A in diameter) with a trilamellar pattern about 80 A thick. Isolated membrane was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, displaying five major protein bands, five minor protein bands, and some protein which remained at the origin. The five major protein components had apparent molecular weights of 54,000, 47,000, 35,000, 31,000, and 28,000. All mastigoneme protein components are glycoproteins as judged by periodic acid-Schiff staining. The mastigoneme preparation contained three major protein bands. Two of them were revealed as doublets and migrated with an average velocity corresponding to 83,000 delatons, the other major protein band migrated with a velocity corresponding to 54,000 daltons. A heavy carbohydrate band is seen near the bromphenol blue tracking dye. The axoneme preparation showed one major protein band having an apparent molecular weight of about 54,000 and some proteins having high molecular weights which remained on top of the polyacrylamide gel.

Animals↗
PubMed1976

The flagellar membrane of Ochromonas danica. Lipid composition.

The lipids of the whole flagella and the flagella membrane of the phytoflagellate Ochromonas danica were isolated and compared with those of the whole cell. The polar lipids were separated by two-dimensional thin layer chromatography. One-dimensional thin layer chromatography was used for the separation of the nonpolar lipids. In all respects the lipids of the whole flagella were identical with those of the flagellar membrane. These methods established the presence in flagellar membrane of the polychlorosulfolipids of O. danica as more than 90 molar per cent of the total polar lipids. These sulfolipids had been previously characterized as 1,14-docosanediol-1, 14-disulfate and 1,15-tetracosanediol-1,15-disulfate, containing zero to six chloro groups substituting for hydrogen on the chain. Seven unknown polar lipids were found. Both phosphorus analysis on each lipid and the molybdenum spray reagent for phospholipids on the chromatogram showed that there is no phospholipid present in O. danica flagellar membrane. Positive reactions to the diphenylamine spray reagent suggest that up to four of the unknown polar lipids are glycolipids. Of these, three reacted positively with ninhydrin. All of the unknown lipids reacted with the acidified 2,4-dinitrophenylhydrazine spray reagent suggesting the presence of aldehyde, ketone, glycoside, or plasmalogen. One unknown substance appeared near the origin of thin layer chromatograms. It showed a positive reaction with Dragendorff reagent, suggesting the presence of a quaternary amine group. This substance is presumed to be nonlipid, since it is not synthesized from [1-14C]acetate under the growth conditions used, as revealed by autoradiograms of thin layer chromatograms. It contained 35% hexose or hexosamine. It is devoid of phosphorus (0.7%) and is less than 4% protein (or phenolic groups or peptide), as judged by the Lowry assay using bovine serum albumin as a standard. Analysis of the nonpolar lipids of the flagellar membrane showed that free fatty acids constitute about 12 molar per cent of the total lipids. These fatty acids could be true components of the membrane or artifacts of the extraction procedure although every precaution was taken to prevent artifactual production of free fatty acids. The sterols constitute nearly 10 molar per cent of total lipids. Sterol esters were absent from the membrane. There are two additional major unknown nonpolar lipids present. The implications of such a high proportion of chlorosulfolipids as a polar lipid component in the membrane are important because of the unique structures of these lipids, which have ionic groups at or near both ends of the aliphatic chain.

Animals↗
PubMedDate not supplied

Evidence for the involvement of ATP in co-translational protein translocation.

Identification of the source of energy for protein translocation across biological membranes is important in understanding the mechanism of this process. In eukaryotic cells, the tight coupling between translation and translocation and firm attachment of the secreting ribosomes to membranes, as well as theoretical calculations, have led to the suggestion that energy derived from protein synthesis is sufficient for protein translocation. On the other hand, in bacterial systems neither the attachment of ribosomes to membrane (other than nascent chains) nor tight coupling of translocation to translocation has been observed. Moreover, certain proteins can be translocated across membranes either at the time of, or after, translation. The separation of protein translocation from translation has made possible the demonstration that ATP hydrolysis is essential for post-translational protein translocation across bacterial membranes and, more recently, also across canine and yeast endoplasmic reticulum membranes. Here we report that certain ATP analogues inhibit co-translational protein translocation at concentrations that do not interfere with protein synthesis, suggesting that ATP is also required for co-translational protein translocation.

Adenosine Triphosphate↗