bluuebunny/crossref_metadata_2025_split huggingface dataset:
Oxygen‐dependent microbicidal systems of phagocytes and host defense against intracellular protozoa
Authors: Locksley Richard M. , Klebanoff Seymour J. 
Published: December 2004

AbstractThe role of oxygen‐dependent microbicidal systems of leukocytes in the host defense against the major nonerythrocytic intracellular protozoa which infect man—Toxoplasma gondii, Trypanosoma cruzi, and the Leishmania species—is reviewed. The hydrogen peroxide‐halide‐peroxidase microbicidal system is uniformly cidal to these organisms in vitro. Peroxidase‐independent oxygen product(s) toxicity is more variable. Studies to date indicate that phagocytes which contain granule peroxidase and which have the capacity to generate a vigorous respiratory burst; eg, neutrophils and monocytes, possess substantial activity against these protozoa. The absence of granule peroxidase together with the markedly attenuated respiratory burst of resident macrophages leaves these cells with a severe microbicidal defect. These protozoa can enter resident macrophages in the absence of antibody and survive and replicate within the intracellular environment. Enhancement of the antiparasite activity of resident macrophages can be accomplished either by activation of these cells by exposure to sensitized T‐cell products, or by the introduction of exogenous peroxidase into the vacuole. Other factors influencing the ability of protozoa to survive intracellularly include the capacity of these organisms to avoid effective triggering of the macrophage respiratory burst and the levels of endogenous scavengers of oxygen products within the parasite.
Radioiodination studies of the envelopes from Xenopus laevis eggs
Authors: Nishihara Tatsuro , Gerton George L. , Hedrick Jerry L. 
Published: December 2004

AbstractTo investigate the molecular basis of the observed morphological and biological characteristics of coelomic egg envelopes (CE), vitelline envelopes (VE), and fertilization envelopes (FE) of Xenopus laevis eggs, envelopes were radioiodinated under a variety of conditions: in situ, isolated and intact, or solubilized. The distribution of 125I in envelope components was analyzed by sodium dodecyl sulfate‐polyacrylamide gel electrophoresis. Each envelope type displayed unique profiles when iodinated in the intact state. A major constituent of VE, the 41,500 molecular weight component, was not labeled in the intact state, although the corresponding component of CE was heavily labeled. After dissociation of the envelope by guanidine‐HCl or sodium dodecyl sulfate, all of the components could be radioiodinated. However, when the envelopes (VE and FE) were dissolved by heating and subsequently radioiodinated by lactoperoxidase, the resulting radioactivity profile was similar to that of the intact envelopes, suggesting that in the heat‐dissolved envelope, the individual components retain similar structural relations as in the intact envelope. Quantitative but not qualitative differences were found between the inner and outer aspects of VE and FE. The significance of these findings is discussed in relation to what is known about the morphological, biological, and molecular properties of the envelopes.
Nuclear protein changes following N,N‐dimethylformamide (DMF)‐induced maturation
Authors: Kimball P. M. , Hixon Sharon 
Published: December 2004

AbstractA human colonic carcinoma cell line was exposed to a nontoxic concentration of N,N‐dimethylformamide (DMF) for 2 wk. Nuclear proteins were isolated from control and treated cells and compared by sodium dodecyl sulfate (SDS) electrophoresis. Qualitative and quantitative differences were observed. Metabolic labeling with tritiated leucine demonstrated qualitative variation between control and treated cells.
Primary photochemistry in the facultative green photosynthetic bacterium Chloroflexus aurantiacus
Authors: Blankenship Robert E. , Feick Reiner , Bruce Barry D. , Kirmaier Christine , Holten Dewey , Fuller R. Clinton 
Published: December 2004

AbstractThe mechanism of primary photochemistry has been investigated in purified cytoplasmic membranes and isolated reaction centers of Chloroflexus aurantiacus. Redox titrations on the cytoplasmic membranes indicate that the midpoint redox potential of P870, the primary electron donor bacteriochlorophyll, is +362 mV. An early electron acceptor, presumably menaquinone has Em 8.1 = −50 mV, and a tightly bound photooxidizable cytochrome c554 has Em 8.1 = +245 mV. The isolated reaction center has a bacteriochlorophyll to bacteriopheophytin ratio of 0.94:1. A two‐quinone acceptor system is present, and is inhibited by o‐phenanthroline. Picosecond transient absorption and kinetic measurements indicate the bacteriopheophytin and bacteriochlorophyll form an earlier electron acceptor complex.
Comparison of the expression‐linked extra copy (ELC) and basic copy (BC) genes of a trypanosome surface antigen
Authors: Donelson John E. , Murphy William J. , Brentano Steven T. , Rice‐Ficht Allison C. , Cain George D. 
Published: December 2004

AbstractA recombinant clone of an expression‐linked extra copy (ELC) gene of a trypanosome‐variable surface glycoprotein was sequenced. In addition the sequences of the corresponding cDNA and portions of the two basic copy genes were determined. Comparison of these sequences reveals that the 5′ boundary of the ELC‐transposed segment (2.2 kb) occurs within a repetitive sequence about 700 bp upstream from the start codon of the coding sequence. This sequence does not contain internal symmetries and is not homologous with the repetitive sequence at the 3′ boundary. The first 35 nucleotides of the cDNA are different than the corresponding ELC sequence and presumably were transcribed from another genomic location. A restriction fragment containing predominantly sequences outside of the 5′ boundary hybridizes to a Pst I fragment whose length is variable in different trypanosome clones. This hybridization pattern is similar to that observed using probes for surface glycoprotein genes that are expressed via the nonduplication‐associatcd (NDA) mechanism rather than the ELC mechanism. This indicates that there is a sequence correlation between these two DNA rearrangement mechanism.
Sorting and recycling of cell surface receptors and endocytosed ligands: The asialoglycoprotein and transferrin receptors
Authors: Ciechanover Aaron , Schwartz Alan L. , Lodish Harvey F. 
Published: December 2004

AbstractWith few exceptions, receptor‐mediated endocytosis of specific ligands is mediated through clustering of receptor‐ligand complexes in coated pits on the cell surface, followed by internalizalion of the complex into endocytic vesicles. During this process, ligand‐receptor dissociation occurs, most probably in a low pH prelysosomal compartment. In most cases the ligand is ultimately directed to the lysosomes, wherein it is degraded, while the receptor recycles to the cell surface.We have studied the kinetics of internalization and recycling of both the asialoglycoprotein receptor and the transferrin receptor in a human hepatoma cell line. By employing both biochemical and morphological/immunocytochemical approaches, we have gained some insight into the complex mechanisms which govern receptor recycling as well as ligand sorting and targeting. We can, in particular, explain why transferrin is exocytosed intact from the cells, while asialoglycoprotcins are degraded in lysosomes. We have also localized the intra‐cellular site at which endocylosed receptor and ligand dissociate.
Fluorescence decay kinetics of chlorophyll in photosynthetic membranes
Authors: Karukstis Kerry K. , Sauer Kenneth 
Published: December 2004

AbstractThe absorption of light by the pigments of photosynthetic organisms results in electronic excitation that provides the energy to drive the energy‐storing light reactions. A small fraction of this excitation gives rise to fluorescence emission, which serves as a sensitive probe of the energetics and kinetics of the excited states. The wavelength dependence of the excitation and emission spectra can be used to characterize the nature of the absorbing and fluorescing molecules and to monitor the process of sensitization of the excitation transfer from one pigment to another. This excitation transfer process can also be followed by the progressive depolarization of the emitted radiation. Using time‐resolved fluorescence rise and decay kinetics, measurements of these processes can now be characterized to as short as a few picoseconds. Typically, excitation transfer among the antenna or light harvesting pigments occurs within 100 psec, whereupon the excitation has reached a photosynthetic reaction center capable of initiating electron transport. When this trap is functional and capable of charge separation, the fluorescence intensity is quenched and only rapidly decaying kinetic components resulting from the loss of excitation in transit in the antenna pigment bed are observed. When the reaction centers are blocked or saturated by high light intensities, the photochemical quenching is relieved, the fluorescence intensity rises several fold, and an additional slower decay component appears and eventually dominates the decay kinetics. This slower (1‐2 nsec) decay results from initial charge separation followed by recombination in the blocked reaction centers and repopulation of the excited electronic state, leading' to a rapid delayed fluorescence component that is the origin of variable fluorescence. Recent growth in the literature in this area is reviewed here, with an emphasis on new information obtained on excitation transfer, trapping, and communication between different portions of the photosynthetic membranes.
Differential protein insertion into developing photosynthetic membrane Regions of Rhodopseudomonas sphaeroides
Authors: Inamine Gordon S. , Reilly Patricia A. , Niederman Robert A. 
Published: December 2004

AbstractPrevious studies have suggested that much of the B800‐850 light‐harvesting bacteriochlorophyll a‐protein complex is inserted directly into the intracytoplasmic photosynthetic membrane of Rhodopseudomonas sphaeroides. In contrast, the B875 light‐harvesting and reaction center complexes are assembled preferentially at peripheral sites of photosynthetic membrane growth initiation. The basis for this apparent site‐specific polypeptide insertion was examined during the inhibition of RNA and protein syntheses. The pulse labeling of polypeptides at the membrane growth initiation sites was significantly less sensitive to inhibition by rifampicin, chloramphenicol, or kasugamycin than in the intfacytoplasmic or outer membranes. This suggests increased stability for the translation machinery at these membrane invagination sites. Similar differential effects in polypeptide insertion were observed during inhibition of bacteriochlorophyll synthesis through deprival of δ‐aminolevulinate to R sphaeroides mutant H‐5, which requires this porphyrin precursor. The pulse‐labeling patterns observed during the inhibition of both RNA and pigment syntheses were consistent with the uncoupling of polypeptide insertion into the membrane invagination sites from their growth and maturation into intracytoplasmic membranes.
A distinct signal peptidase for prolipoprotein in escherichia coli
Authors: Tokunaga Masao , Loranger Judith M. , Wu Henry C. 
Published: December 2004

AbstractWe have previously demonstrated the modification and processing of Escherichia coli prolipoprotein (Braun's) in vitro (Tokunaga M, Tokunaga H. Wu HC: Proc Natl Acad Sci USA 79:2255, 1982). Using this in vitro assay of prolipoprotein signal peptidase and globomycin selection, we have isolated and partially characterized an E coli mutant which contained a higher level of prolipoprotein signal peptidase activity. In contrast, the procoat protein signal peptidase activity was not increased in this mutant as compared to the wild‐type strain. Furthermore, E coli strains containing cloned procoat protein signal peptidase gene were found to contain elevated levels of procoat protein signal peptidase, but normal levels of prolipoprotein signal peptidase. These two signal peptidase activities were also found to exhibit different stabilities during storage at 4°C. Thus biochemical, immunological, and genetic evidence clearly indicate that prolipoprotein signal peptidase is distinct from procoat protein signal peptidase in E coli.
ATP‐released large subunits participate in the assembly of RuBP carboxylase
Authors: Milos Patrice , Roy Harry 
Published: December 2004

AbstractPreincubation of 35S‐methionine‐labeled chloroplast extracts with ATP at 0°C potentiates the subsequent assembly of labeled large subunits into RuBPCase. This is correlated with the dissociation of newly synthesized large subunits from the 29S large subunit binding protein complex. These released large subunits then assemble into RuBPCase in a second, nucleotide‐stimulated reaction. The data demonstrate that the 29S complex can play an active role in the assembly of RuBPCase.
Adaptive reorganization of protein and lipid components in chloroplast membranes as associated with herbicide binding
Authors: Mattoo Autar K. , St. John Judith B. , Wergin William P. 
Published: December 2004

AbstractCultivation of Spirodela oligorrhiza (Kurtz) Hegelm on a sublethal dose of atrazine results in a higher linolenic to linoleic acid ratio in the thylakoid membrane lipids, less starch, more osmiophilic globules, and a reduced stroma lamellar system. Also, the grana become randomly oriented and contain more numerous and elongated lamellae. These alterations in the lipid composition and ultrastructure of the chloroplast resemble those previously observed in triazine‐resistant weed biotypes and in chloroplasts developed under low light. Thylakoid membranes from atrazine‐adapted plants revealed an additional high‐affinity binding constant for [14C]‐diuron but the number of diuron binding sites actually decreased by 20 times compared to controls. The 32,000‐dalton membrane protein of the chloroplast is synthesized actively, but its breakdown appears decreased compared to control plants. The adaptive reorganization of thylakoid components may be a compensatory mechanism for maintenance of a functional interaction of the proteins and lipids of the photosystem II complex.
Fate of surface immunoglobulin during induction of lymphocyte proliferation
Authors: Ramanadham Madduri , Gollapudi Sastry V. S. , Kern Milton 
Published: December 2004

AbstractThe modulation of immunoglobulin on the surface of rabbit B lymphocytes by goat antibodies with specificity for rabbit surface membrane immunoglobulin or by such goat antibodies covalently linked to Sepharose was studied in relation to the proliferative response to these agents. Although the induction of DNA synthesis was greater in the presence of Sepharose‐linked antibody than in the presence of free antibody, modulation of surface membrane immunoglobulin was induced with free but not with Sepharose‐linked antibody. Thus, in the presence of free antibody the surface membrane immunoglobulin content of cells was rapidly decreased and remained at a low level throughout the culture period, whereas the surface immunoglobulin content of cells incubated with Sepharose antibody was essentially unaltered. The surface immunoglobulin lost from cells incubated with free goat antibodies reappeared slowly upon further incubation in culture medium devoid of antibody, and such reappearance of rabbit surface membrane immunoglobulin was inhibited by puromycin. Upon culture with Sepharose‐linked antibody the surface membrane immunoglobulin content of B cells was unaffected by puromycin. This result was interpreted as indicating that surface membrane immunoglobulin loss followed by reappearance does not occur. Lastly, the linkage of surface membrane immunoglobulin to cytoskeletal elements induced by free antibody was not induced by Sepharose‐linked antibody as judged from differences in detergent solubilization characteristics. Possible mechanisms to account for these differences in surface membrane immunoglobulin modulation as they relate to the proliferative response are considered.
Correlation of structure and function of chloroplast membranes at the supramolecular level
Authors: Staehelin L. Andrew , DeWit Marcia 
Published: December 2004

AbstractFreeze‐fracture electron microscopy has revealed that different size classes of intramembrane particles of chloroplast membranes are nonrandomly distributed between appressed grana and nonappressed stroma membrane regions. It is now generally assumed that thylakoid membranes contain five major functional complexes, each of which can give rise to an intramembrane particle of a defined size. These are the photosystem II complex, the photosystem I complex, the cytochrome f/b6 complex, the chlorophyll a/b light‐harvesting complex, and the CF0‐CF1 ATP synthetase complex. By mapping the distribution of the different categories of intramembrane particles, information on the lateral organization of functional membrane units of thylakoid membranes can be determined. In this review, we present a brief summary of the evidence supporting the correlation of specific categories of intramembrane particles with known biochemical entities. In addition, we discuss studies showing that ions and phosphorylation of the membrane adhesion factor, the chlorophyll a/b light‐harvesting, complex, can affect the lateral organization of chloroplast membrane components and thereby regulate membrane function.
Molecular species of epidermal growth factor carrying immunosuppressive activity
Authors: Koch J. H. , Fifis T. , Bender V. J. , Moss B. A. 
Published: December 2004

AbstractThe suppression of antibody formation to sheep red cells in mice by partially purified fractions of mouse submaxillary gland [7] was shown to be caused by epidermal growth factor (EGF). Purification of EGF by the method of Savage and Cohen [11] resolved three components referred to as EGF a, EGF b, and EGF c. All three induced premature eye opening in neonatal mice, but only EGF a (identified as EGF1‐53 ) had full immunosuppressive activity. EGF c was shown by micropeptide mapping of chymotryptic and thermolytic digests and aminoterminal analysis to differ from EGF a only by the presence of β‐aspartyl instead of an asparaginyl residue. EGF b differed from EGF a in that it lacked the N‐terminal asparagine. EGF shortened enzymatically at its carboxy terminal by two or five amino acids did not have any immunosuppressive activity. These findings‐suggest that, in contrast to some other biological effects of EGF, intact amino and carboxy terminals are required for the expression of immunosuppressive activity.
Stimulation of glycosaminoglycan production in murine tumors
Authors: Knudson Warren , Biswas Chitra , Toole Bryan P. 
Published: December 2004

AbstractThree types of murine tumors, B‐16 melanoma, A‐10 carcinoma, and S‐180 sarcoma, were shown to contain elevated glycosaminoglycan (GAG) concentrations in vivo as compared to normal muscle or subcutaneous tissue. Hyaluronate was especially concentrated in the A‐10 carcinoma, which contained approximately six times more hyaluronate than subcutaneous tissue and 18 times more than muscle. In all three tumors, chondroitin sulfates, especially chondroitin‐4‐sulfate, were present in higher concentrations than in the. normal tissues. In culture, however, all three tumor cell lines produced less than 5% as much GAG as mouse fibroblasts, when measured by incorporation of [3H] acetate or by chemical analysis. Varying the culture passage number or the medium composition, ie, glucose, serum, and insulin concentrations, had little effect on GAG synthesis by the tumor cells. The low GAG levels in the tumor cell cultures were not due to hyaluronidase activity in their media. In an attempt to mimic possible host‐tumor cell interactions that could account for the elevated GAG levels in vivo, tumor cells were cocultured with fibroblasts, but no stimulation above the amount made by the tumor cells alone plus that by the fibroblasts alone was observed. Conditioned media from the tumor cells, either dialyzed or not against fresh complete medium, had no effect on fibroblast GAG synthesis. Tumor extracts, however, were found to stimulate synthesis of hyaluronate by fibroblasts. Stimulation by extracts of A‐10 carcinoma was greater than and additive to that of serum. The above results strongly suggest that GAG production in these tumors is in pail regulated by host‐tumor interactions.
Enzymatic characteristics of pp60v‐src isolated from vanadium‐treated transformed cells
Authors: Collett Marc S. , Belzer Susan K. , Kamp Lisa E. 
Published: December 2004

AbstractThe transforming protein of Rous sarcoma virus (RSV) typically appears as a single phosphorylated polypeptide designated pp60v‐src, pp60v‐src possesses a protein kinase activity specific for tyrosine residues on select protein substrates. Treatment of RSV‐transformed cells with vanadium ions resulted in the appearance of an electrophoretic variant of pp60v‐src and was paralleled by a significant increase in the src kinase specific activity in purified enzyme preparations. Both the normal (standard) src kinase and the src kinase preparations obtained from vanadium‐treated cells exhibited similar optimal activity profiles for MgCl2, KCl, and pH. Furthermore, their site specificities of phosphorylation of the substrates casein and vinculin were the same. The reaction kinetic profile of the standard src kinase showed a nonlinear pattern, while the vanadium enzyme exhibited conventional linear Michaelis‐Menten kinetics. These results are discussed with respect to the possible functional regulation of pp60v‐src activity by a vanadium‐sensitive protein phosphatase activity.
A 38 base pair insertion in the proα2(I) collagen gene of a patient with Marfan syndrome
Authors: Henke Elizabeth , Leader Mark , Tajima Shingo , Pinnell Sheldon , Kaufman Russel 
Published: December 2004

AbstractAbnormalities in type I collagen have been recognized in a number of connective tissue disorders. In the Marfan syndrome, an autosomal dominant condition producing a generalized abnormality in connective tissue, no consistent abnormality has been identified, although one individual has been found to have an elongated proα2(I) collagen chain [Byers et al, Proc Natl Acad Sci USA 78:7745, 1981]. To determine the nature of the alteration in the gene that produced this abnormality, we studied the proα2(I) gene from this individual by genomic blotting and gene cloning. Genomic mapping studies detected no abnormalities. However, analysis of the cloned segment of the proα2(I) collagen gene from the Marfan individual indicates that the gene contains a 38 base pair insertion in an intron near the collagenase cleavage site. Although the relationship of this insertion to the protein abnormality is unclear, it may be a useful marker for the diagnosis of the Marfan syndrome.