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At least 829 records · Page 46Linked to original sources
PubMed1983

Polymorphism of phosphatidylethanolamine-phosphatidylserine model systems: influence of cholesterol and Mg2+ on Ca2+-triggered bilayer to hexagonal (HII) transitions.

Previous work has shown that Ca2+ can trigger bilayer to hexagonal (HII) polymorphic phase transitions in (unsaturated phosphatidylserine (PS)-phosphatidylethanolamine (PE) model systems. In this work we examine the influence of cholesterol and Mg2+ on the phase preferences of PS-PE systems. Subsequently, the influence of cholesterol and Mg2+ on the levels of Ca2+ required to trigger bilayer-HII transitions in these mixed systems is studied. It is shown that at 30 degrees C the presence of equimolar (with respect to phospholipid) levels of cholesterol engenders formation of the HII phase for PE-PS systems containing 15 and 30 mol% PS, whereas bilayer structure is maintained for PE-PS-cholesterol (1:1:2) dispersions. However, the polymorphic phase preferences of the latter system are much more sensitive to the presence of monovalent and divalent cations. In the absence of cholesterol, Mg2+ and high salt concentrations do not affect the polymorphic phase preferences of PE-PS (1:1) systems. In contrast, 8 mM or higher Mg2+ levels or salt concentrations greater than 1.0 M induce HII-phase formation in PE-PS-cholesterol (1:1:2) systems. Further, lower Mg2+ concentrations (2 mM) act as a powerful adjunct to Ca2+ triggering of HII-phase structure in such systems, reducing the Ca2+ concentration required from 4 to 0.25 mM. These results are discussed in terms of Ca2+ concentrations required for fusion events and the influence of cholesterol on the structural preferences of the inner monolayer lipids of the erythrocyte membrane.

Calcium↗
PubMed2001

Effect of amino acids on goat cauda epididymal sperm cryopreservation using a chemically defined model system.

Studies were carried out to analyze the cryoprotecting efficacy of several amino acids by use of a chemically defined synthetic medium (modified Ringer's solution) and goat cauda epididymal sperm as the model system. Motile goat cauda sperm dispersed in the synthetic medium were subjected to a freezing protocol in a computer-controlled bio-freezer, cooling 0.25 degrees C x min(-1) to 5 degrees C, 5 degrees C x min(-1) to -20 degrees C, and 20 degrees C x min(-1) to -100 degrees C, prior to being plunged into liquid nitrogen. In the absence of amino acids, sperm cells completely lost their flagellar motility. Of all the amino acids tested, l-alanine showed maximal cryoprotection potential. l-Alanine at 135 mM offered optimum cryoprotection potential: recovery of sperm forward motility and total motility were 14 +/- 2% and 19 +/- 2%, respectively. l-Glutamine, l-proline, and glycine at optimum concentration (100-150 mM) cryopreserved approx. 11-17% total motility of the sperm cells, whereas amino acids such as l-arginine, l-lysine, and l-histidine offered little cryoprotection (0-5%) to the cells. Increasing the amino acid concentration beyond the optimum level sharply decreased the recovery of the sperm motility, which therefore showed a biphasic cryoprotection profile. Addition of amino acids enhanced (approx. 7-10%) the cryoprotection efficacy of the well-known cryoprotectants glycerol and a combination of glycerol and dimethyl sulfoxide. The presence of glycerol caused a marked reduction (from 100-150 mM to 20-70 mM levels) in the optimal cryoprotective concentration of the amino acids. The combined cryoprotecting action of glycerol, dimethyl sulfoxide, and amino acids provided motility recovery as high as 52%. The observation that amino acids and dimethyl sulfoxide had an additive effect in augmenting the cryoprotecting potential of glycerol suggests that the mechanism of their action is different from that of glycerol. This cocktail of cryoprotectants may be useful for cryopreservation of semen of various species.

Amino Acids↗
PubMed1987

Postembedding light- and electron microscopic immunocytochemistry of amino acids: description of a new model system allowing identical conditions for specificity testing and tissue processing.

Specificity testing should be performed under conditions identical to or closely similar to those of the immunocytochemical procedure. This paper describes a new model system that meets this requirement for postembedding immunocytochemistry of amino acids at the light- and electron microscopic levels. Test conjugates, obtained by reacting different amino acids with brain macromolecules in the presence of glutaraldehyde, were freeze-dried and embedded in an epoxy resin (Durcupan) exactly as for brain tissue. One section from each of the embedded amino acid conjugates and from a brain protein-glutaraldehyde conjugate (without amino acid) were piled on top of each other and embedded anew. Transverse semithin (0.5 micron) and ultrathin sections were cut through the stack. These test sections, in which all the different conjugates were represented, were then processed in the same drops of sera as the tissue sections to permit identical conditions for testing and immunocytochemistry. After immunogold labelling for electron microscopy, a quantitative expression of crossreactivity was obtained by computer-assisted calculation of gold particle densities over the different conjugates. The antisera used in the present study (glutamate antiserum 13, taurine antiserum 20, and GABA antiserum 26) showed highly selective labelling of the respective amino acid conjugates and produced distinct labelling patterns in simultaneously processed cerebellar sections.

Amino Acids↗
PubMed1994

Map-based cloning in crop plants: tomato as a model system II. Isolation and characterization of a set of overlapping yeast artificial chromosomes encompassing the jointless locus.

A map-based cloning technique for crop plants is being developed using tomato as a model system. The target gene jointless is a recessive mutation that completely suppresses the formation of flower and fruit pedicel abscission zones. Previously, the jointless locus was mapped to a 3 cM interval between the two molecular markers TG523 and RPD158. Physical mapping of the jointless region by pulsed-field gel electrophoresis demonstrated that TG523 and RPD158 reside on a 600 kb SmaI fragment. In this study, TG523 was used as a probe to screen a tomato yeast artificial chromosome (YAC) library. Six tomato YAC (TY) clones were isolated, ranging from 220 to 380 kb in size. Genetic mapping of YAC ends demonstrated that this set of overlapping YACs encompasses the jointless locus. Two YAC ends, TY159L (L indicates left end) and TY143R (R indicates right end), cosegregate with the jointless locus. Only one of the six YACs (TY142) contained single-copy DNA sequences at both ends that could be mapped. The two ends of TY142 were mapped to either side of the jointless locus, indicating that TY142 contains a contiguous 285 kb tomato DNA fragment that probably includes the jointless locus. Physical mapping of the TY142 clone revealed that TY159L and TY143R reside on a 55 kb SalI fragment. Southern blot hybridization analysis of the DNAs of tomato lines nearly isogenic for the jointless mutation has allowed localization of the target locus to a region of less than 50 kb within the TY142 clone.

Base Sequence↗
PubMed2004

Cholesterol modulates maculosin's orientation in model systems of biological membranes. Relevance towards putative molecular recognition.

Fluorescence techniques were used to study (1) the extent of insertion of the bioactive cyclic dipeptide cyclo(l-tyrosyl-l-prolyl), maculosin, in model systems of membranes of 1, 2-palmitoyl-sn-glycero-3-phosphatidyl choline (DPPC) or 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidyl choline (POPC), (2) its in-depth location in those lipidic membranes, and (3) the influence of cholesterol on the dipeptides's location and orientation. Partition into lipidic bilayers is extensive, mainly for liquid crystalline phase membranes (K(p)=1.3x10(4)). Maculosin locates at the lipid head groups level regardless of the membrane system. Nevertheless, its orientation is lipid phase dependent. When maculosin was inserted in liquid crystalline phase bilayers, its phenolic ring was perpendicular to the membrane surface, whereas it changed orientation when inserted in gel phase membranes. Cholesterol was able to reverse the lipid phase influence on maculosin's orientation.

Anisotropy↗
PubMed1992

252Cf plasma desorption mass spectrometry in the synthesis of porphyrin model systems.

252Cf plasma desorption mass spectrometry has been used in the characterization of more than 100 synthetic porphyrins ranging in mass from 614 u for tetraphenylporphyrin to over 2000 u for some porphyrin model systems. In virtually every case, 252Cf plasma desorption mass spectrometry yielded an intense ionized molecule ion [M.+ and/or (M+H)+], irrespective of the groups appended to the porphyrin. The appended groups include carboxylic acids, amides, imides, chloroacetamides, Fmoc-protected amino acids, aromatic amines, nitriles, alkynes, alkenes, esters, active esters, benzyl ethers, acetals, dithioacetals, ketones, imines, phenols, quinone, hydroquinone, ferrocene, cyanine dyes, trimethylsilyl protecting groups, nitro groups, and combinations of these functionalities. Metalloporphyrins and porphyrin-porphyrin dimers are also analyzed with ease. Resolved isotopic peaks were observed for porphyrins with molecular weights below 1000, and unresolved isotopic peaks yielding average masses were observed for porphyrin compounds with higher molecular weights. The limited resolution in the higher molecular weight range does not lessen the utility of the method because the observation of the molecule ions [M.+ and/or (M+H)+] provides unambiguous evidence concerning the success of the synthesis. The 252Cf plasma desorption mass spectra of porphyrins are not complicated by chemical transformations. This method is ideally suited for rapid analysis of synthetic porphyrins and provides a powerful tool for chemists engaged in the synthesis of complex organic molecules.

Californium↗
PubMed2005

Correlation of acrylamide generation in thermally processed model systems of asparagine and glucose with color formation, amounts of pyrazines formed, and antioxidative properties of extracts.

The relations between the formation of acrylamide and color, pyrazines, or antioxidants in an asparagine/d-glucose browning model system under various conditions were investigated. The highest level of acrylamide was produced in the asparagine/glucose (1:3) system heated at 170 degrees C for 30 min (2629 microg/g asparagine). Color intensity increased with temperature and heating time. The formation of pyrazines increased steadily with an increase of temperature (140-170 degrees C) and heating time (15-60 min). Antioxidant formation varied among the samples heated under different conditions. A clear correlation between formation of acrylamide and browning color was obtained. The formation of acrylamide was linearly correlated with the formation of total pyrazines during the initial stages of the Maillard reaction. No obvious correlation between formation of acrylamide and antioxidants was observed. However, excess amounts of asparagine increased the formation of antioxidants, whereas excess amounts of glucose reduced its formation.

Acrylamides↗
PubMed1993

A model system for in vivo gene transfer into the central nervous system using an adenoviral vector.

Previous methods of in vivo gene transfer to differentiated neurons of the adult mammalian brain have been inefficient and associated with technical problems. We have therefore developed a model system of direct gene transfer using a replication-defective adenoviral vector containing a beta-galactosidase gene to transduce brain neurons. Following injection of purified high titre recombinant adenovirus into the caudate putamen of seven week old mice, lacZ activity was evident in neural components of the central nervous system (CNS) for at least 8 weeks post infection. The efficiency of adenoviral gene transfer was very high compared to other techniques, suggesting an attractive and efficient alternative for neuronal gene transfer in vivo.

Adenoviridae↗
PubMed2006

Examination of conditions inhibiting the formation of acrylamide in the model system of fried potato.

Acrylamide (AAm) is produced in food through the reaction of asparagine and reducing sugar. We examined several methods of reducing the level of AAm using potato tubers. The fried model system that we employed consisted of thin slices that were first treated in water under different conditions before frying. A sufficient amount of water present in the fry material acts as an inhibitor against the formation of AAm and allows only a negligible amount of AAm to form. It was found that given the low content of water, the fry material temperature was sufficiently high to allow a relatively large level of AAm to form. Examination of water treatment prior to frying revealed that higher-temperature treatment water and longer treatment time resulted in the formation of lower levels of AAm. Moreover, removing some of the residual heat had an inhibiting effect on the formation of AAm.

Acrylamide↗
PubMed1992

Effect of cortisol on the secretion of testosterone and estradiol-17 beta by human granulosa-luteal cell cultures. A model system for analyzing hormonal alterations in female athletes.

The combination of hypercortisolism and usually low androgen and estrogen levels is frequently observed in female long distance athletes. In order to find a useful model system for studying the underlying mechanisms, the following studies were performed. The effect of cortisol on the secretion of testosterone (T) and estradiol-17 beta (E2) by human granulosa-luteal cells was studied in vitro in cultures of cells recovered from mature follicles of gonadotrophin stimulated women (participating in the IVF program). Following 24 hours of culture in tissue culture medium without hormonal additives, the granulosa-luteal cells were incubated for 6 hours in media with addition of 4-androstene-3,17-dione (A-4) as precursor and hMG and cortisol in different combinations. The secretion of T was significantly stimulated by cortisol but not by human menopausal gonadotrophin (hMG). Cortisol, but not hMG, also increased the secretion of E2, although this effect was not statistically significant. These in vitro findings make a direct effect of cortisol upon ovarian sex steroid secretion less likely as the mechanism behind the subnormal sex steroid levels in female long distance athletes. Instead, inadequate gonadotrophic stimulation, related to hypothalamic amenorrhea, and/or a selective decrease in the adrenal secretion of precursor steroids, may be an explanation.

Estradiol↗
PubMed2001

Toward a molecular understanding of psychostimulant actions using genetically engineered dopamine receptor knockout mice as model systems.

A major focus in studying the progression and prevention of addictive diseases has been to understand the molecular and cellular mechanisms underlying drug addiction. The brain dopaminergic system plays a central role in reward and motivation and is thought to be the main neural substrate for the actions of abusive drugs. We have used the gene targeting technology to generate dopamine D1 and D3 receptor knockout mice and used these mice as model systems to gain a molecular understanding of acute effects of psychostimulants cocaine and amphetamine. The use of a combined approach involving behavioral, electrophysiological as well as molecular studies has allowed us to define initially the roles of dopamine D1 and D3 receptors in the acute effects of psychostimulants and will enable us to understand mechanisms underlying their chronic actions in the future.

Amphetamine↗
PubMed2006

Model systems for beta-hairpins and beta-sheets.

beta-Sheets and alpha-helices are the two principal secondary structures in proteins. However, our understanding of beta-sheet structure lags behind that of alpha-helices, largely because, until recently, there was no model system to study the beta-sheet secondary structure in isolation. With the development of well-folded beta-hairpins, this is changing rapidly. Recent advances include: increased understanding of the relative contributions of turn, strand and sidechain interactions to beta-hairpin and beta-sheet stability, with the role of aromatic residues as a common subtheme; experimental and theoretical kinetic and thermodynamic studies of beta-hairpin and beta-sheet folding; de novo protein design, including all-beta structures, mixed alpha/beta motifs and switchable systems; and the creation of functional beta-hairpins.

Models, Molecular↗
PubMed1997

A model system in haematology and immunology: the human monocytic cell line MONO-MAC-1.

MONO-MAC-1 is a human cell line with properties of blood monocytes, which can be used as a model system to study monocytic functions in vitro. In the present study, we prepared a karyotype of MONO-MAC-1, analysed the growth behaviour, determined the presence of differentiation-associated antigens and studied the expression and secretion of several cytokines upon stimulation with 12-O-tetradecanoyl phorbol 13-acetate (TPA) and lipopolysaccharide (LPS). The MONO-MAC-1 cells have a near diploid karyotype and contain several recurrent chromosomal rearrangements, in particular the translocation (9;11) commonly found in AML-M5. Stimulation with TPA or LPS induced changes in morphology and gene expression, especially an increase in the level of the differentiation marker CD14 and the production of monocyte-related cytokines. Both biomodulators alone were sufficient to promote TNF alpha release; however, the combination of TPA and LPS resulted in a synergistic increase of TNF alpha secretion. Northern blot analysis indicated that upregulated production of TNF alpha was due to induced synthesis of mRNA. The mRNA accumulation peaked approximately 2 h after stimulation and maximum levels of TNF alpha were found in the supernatants after 4-8 h of culture. The MONO-MAC-1 cells could not be restimulated with the same inducer to release TNF alpha when a 48 h pre-treatment was carried out with LPS or TPA. LPS induced the release of granulocyte colony-stimulating factor (G-CSF), while TPA failed to do so. Vice versa, secretion of macrophage CSF (M-CSF) could be induced by TPA, but not by LPS. However, LPS enhanced the TPA-induced M-CSF production. Similarly, incubation of MONO-MAC-1, simultaneously with TPA and LPS, led to granulocyte macrophage CSF (GM-CSF) and interleukin-1beta (IL-1beta)secretion, while both stimulators alone had almost no (TPA) or only a weak (LPS) effect on the secretion of GM-CSF and IL-1beta. Our results demonstrate that MONO-MAC-1 is a unique cell line with distinct monocytic features; certain monocytic properties can be upregulated by activation of intracellular signalling pathway(s). We suggest that, besides the LPS receptor CD14, activation of PKC participates in these process, especially in the production and secretion of cytokines by MONO-MAC-1 cells.

Cell Line↗
PubMed2006

A simple model system for age-dependent DNA damage and cancer.

Aging is the major risk factor for many human cancers. However, the mechanisms responsible for the effect of aging on tumor incidence are poorly understood, in part because few model systems are available to study age-dependent genomic instability. Furthermore, the role of DNA mutations in "normal aging" and "life span extension" is unclear. Our laboratory has developed a novel method to study aging in yeast based on the survival of non-dividing populations (chronological life span). Two major pathways have been identified that control chronological aging: the Ras/PKA/Msn2/4 and the Sch9 pathways. The downregulation of either of them promotes life span extension. Importantly, similar pathways (insulin/IGF-I-like), regulate longevity in higher eukaryotes suggesting a common evolutionary origin for the life span-regulatory mechanisms. Moreover, both Ras and Sch9 are functional homologs of two major mammalian oncogenes (Ras and Akt), which underlines the close link between cancer and aging. By combining chronological life span with simple assays for the detection of DNA mutations and dedifferentiation we have developed a powerful system to identify genes that regulate genomic instability and understand the fundamental mechanisms that may be responsible for age-dependent DNA mutations and cancer in mammals. Here, we describe the use of this system to monitor the age-dependent accumulation of different types of DNA mutations including base substitutions, frame-shift mutations, and gross chromosomal rearrangements (GCRs).

Aging↗
PubMedDate not supplied

Effects of free and liposome-encapsulated hemoglobin on choroidal vascular plexus blood flow, using the rabbit eye as a model system.

PURPOSE: This study investigated the vasoconstrictive effects of both stroma-free and liposome-encapsulated cross-linked hemoglobin (Hb) on vascular plexus hemodynamics, using the choroid of the rabbit eye as a model system. METHODS: Sequential subtraction of high-speed ICG fluorescence angiogram images facilitated visualization of the time-varying patterns of blood flow distribution in the choriocapillaris during the cardiac cycle. Differences between baseline and post-hemoglobin injection blood flow distributions were analyzed. Likewise, differences in the time-varying patterns of flow distribution between the particulate and liquid phases of blood during a cardiac cycle were investigated, since this may bear on differences in vasoactivity induced by circulating stroma-free vs. encapsulated Hb. RESULTS: Cross-linked Hb induced a transient, but marked, localized reduction in choriocapillaris blood flow. This effect was significantly attenuated when liposome encapsulated cross-linked hemoglobin was administered. Plexus blood flow distribution was different for particulate and liquid ICG. CONCLUSIONS: Differences in particulate and liquid ICG flow patterns suggest that one contribution to the different plexus blood flow patterns observed in the encapsulated and free Hb experiments may be due to differences in liquid and particle-bound Hb distribution within the plexus. The observed choriocapillaris blood flow reductions may be attributable to an aggregate endothelial cell contractility induced by presence of extra-cellular Hb in the choriocapillaris plexus.

Animals↗
PubMed2000

Androgen deprivation of the PC-310 [correction of prohormone convertase-310] human prostate cancer model system induces neuroendocrine differentiation.

Neuroendocrine (NE) cells are androgen-independent cells and secrete growth-modulating neuropeptides via a regulated secretory pathway (RSP). We studied NE differentiation after androgen withdrawal in the androgen-dependent prostate cancer xenograft PC-310. Expression patterns of chromogranin A, secretogranin III, and prohormone convertase-1 were analyzed at both protein and mRNA level to mark the kinetics of NE differentiation both in vivo and in vitro. PC-310 tumor-bearing nude mice were killed at 0, 2, 5, 7, 14, and 21 days postcastration. PC-310C cultures initiated from collagenase-treated tumor tissue could be maintained up to four passages, and androgen-deprivation experiments were performed similarly. PC-310 tumor volumes decreased by 50% in 10 days postcastration. Proliferative activity and prostate-specific antigen (PSA) serum levels decreased to zero postcastration, whereas PSA levels in PC-310C culture media first decreased and subsequently increased after 5 days. In vivo, androgen receptor (AR) expression decreased initially but returned to control level from 5 days postcastration on. CgA, secretogranin III, and secretogranin V expression increased in vivo from 5 days postcastration on. Subsequently, prohormone convertase-1 and peptidyl alpha-amidating monooxygenase as well as the vascular endothelial growth factor were expressed from 7 days postcastration on, and, finally, growth factors such as gastrin-releasing peptide and serotonin were expressed in a small part of the NE cells 21 days postcastration. The PC-310 tumors did not show colocalization of the AR on the NE cells in the tumor residues after 21 days. As in the PC-310 xenograft, NE differentiation was induced and AR expression relapsed after prolonged androgen suppression in PC-310C. For PC-310C cells, this relapse was associated with the secretion of PSA. PC-310C is the first culture of human prostatic cancer cells having the NE phenotype. The PC-310 model system is a potential androgen-dependent model for studying the role of NE cells in the progression of clinical prostate cancer. Androgen deprivation of NE-differentiated prostate cancer may induce the formation of both NE- and AR-positive dormant tumor residues, capable of actively producing NE growth factors via a RSP, possibly leading to hormone refractory disease.

Androgens↗
PubMed1992

Hammerhead ribozyme cleavage of hamster prion pre-mRNA in complex cell-free model systems.

The cleavage properties of a trans-acting hammerhead ribozyme targeted 51 bases upstream of the putative splicing branch point in the hamster prion pre-mRNA intron were investigated in cell-free model systems in vitro. The specificity of cleavage was demonstrated by the inability of this ribozyme to cleave a non-homologous synthetic message encoding part of the beta amyloid peptide precursor, beta APP, and by the inability of the prion pre-mRNA to be cleaved by a ribozyme targeted to beta amyloid peptide precursor mRNA. Also, the addition of total RNA isolated from rat brain had only a minimal effect on the cleavage of the prion substrate pre-mRNA by the ribozyme. Finally neither the presence of 100 ng of nuclear or cytoplasmic proteins were found to affect the rate of cleavage in vitro.

Adenosine Triphosphate↗