bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhanced binding of phospholipase-A2-modified low density lipoprotein by human adipocytes
Authors: Natarajan Madhu K. , Fong Bessie S. , Angel Aubie
Published: December 2009

Recognition of low density lipoprotein (LDL) by human adipocytes is not dependent on the classical LDL (apoprotein B–E) receptor. To assess whether LDL phospholipids have a role in adipocyte-LDL interactions, binding studies were carried out with human LDL modified with cobra venom phospholipase A2 (PLA2) and freshly isolated adipocytes and purified adipocyte plasma membranes prepared from surgical biopsies. LDL incubated with PLA2 showed increased monoacylphospholipid content, decreased diacylphospholipid content, and increased anodic migration on agarose gel electrophoresis. LDL cholesterol, triglyceride, and protein content remained unchanged. Typically, modification of 16 and 47% of LDL phospholipids enhanced specific binding of 125I-labelled LDL to plasma membranes progressively from 3.1 μg LDL bound/mg membrane protein (control) to 5.8 and 28.2 μg LDL bound/mg membrane protein, respectively. Nonspecific binding was not altered significantly. Excess unlabelled native LDL and high density lipoprotein (HDL3) effectively inhibited binding of PLA2-modified LDL. Freshly isolated adipocytes also showed enhanced binding and uptake of PLA2-modified LDL (0.1 vs. 0.9 μg LDL/(106 cells∙2 h), control vs. modified). The results demonstrate that alterations of LDL phospholipids significantly enhance LDL binding and suggest a regulatory role for phospholipids in lipoprotein–cell interaction. Furthermore, the results support the view that human adipose tissue may be involved in the metabolism of modified lipoproteins, in vivo.Key words: low density lipoprotein, adipocyte, phospholipase, lipoprotein receptors.
Structural studies of the O-chains of the lipopolysaccharides produced by strains of Actinobacillus (Haemophilus) pleuropneumoniae serotype 5
Authors: Altman Eleonora , Griffith Douglas W. , Perry Malcolm B.
Published: December 2009

The water-phase lipopolysaccharides isolated by phenol–water extraction from the cells of four strains of Actinobacillus pleuropneumoniae serotype 5 (K17, L20, B78-3760, and 81-750) were shown on structural analysis to have O-chain components with the same basic polysaccharide structure of a linear unbranched homopolymer of 1,6-linked β-D-galactopyranosyl residues, although the linear length of the O-chain varied among different strains. While those of strains B78-3760 and 81-750 were partially O-acetylated, the O-chains of strains K17 and L20 were unsubstituted.Key words: Actinobacillus pleuropneumoniae, polysaccharide, lipopolysaccharide, pleuropneumonia.
Induction of cell-specific ribosomal proteins in aggregation-competent nonmorphogenetic Dictyostelium discoideum
Authors: Ramagopal S.
Published: December 2009

Vegetatively growing amoebae, if shaken in a starvation (nonnutrient) buffer, acquire aggregation competence, but do not embark on a morphogenetic program. The quantitative variation of ribosomal proteins in vegetative and aggregation-competent cells was compared by labeling the different cell types with [35S]methionine. Vegetative cells were examined at various phases of the growth cycle. No changes could be detected in the content of ribosomes or the apparent stoichiometry of ribosomal proteins in growing cells. In stationary phase cells, the net ribosome content declined to 15% of that observed in logarithmic phase, but the relative amounts of individual ribosomal proteins were not altered. Although aggregation-competent cells contained 30% less ribosomes compared with logarithmic phase cells, the total fraction of newly made ribosomal proteins was the same in both. In contrast to vegetative cells, distinct changes were induced in the ribosomal proteins of aggregation-competent cells. The composition of ribosomes in aggregation-competent phase resembled in every respect that observed in spore cells. As reported earlier, changes were found in all 12 of the developmentally regulated ribosomal proteins. For the majority of newly made ribosomal proteins during aggregation competence, the stoichiometry was similar to that in logarithmically growing cells. However, the relative synthesis of some was particularly higher (13- to 46-fold for A and L; 3- to 8-fold for D, E, S24, L3, S6, and L4) compared with logarithmic phase cells. About 18 proteins, which included the cell-specific ribosomal proteins L18, S10, S14, S16, and L11, were synthesized in lesser amounts than in logarithmic phase cells. It is concluded that the attainment of aggregation competence is sufficient for the induction of spore cell specific ribosomal proteins in Dictyostelium discoideum.Key words: cellular slime mold, ribosomal proteins, development.
Purification and some properties of a thermostable DNA polymerase from a Thermotoga species
Authors: Simpson H. D. , Coolbear T. , Vermue M. , Daniel R. M.
Published: December 2009

A stable DNA polymerase (EC 2.7.7.7) has been purified from the extremely thermophilic eubacterium Thermotoga sp. strain FjSS3-B.1 by a five-step purification procedure. First, the crude extract was treated with polyethylenimine to precipitate nucleic acids. The endonuclease activity coprecipitated. DEAE-Sepharose, CM-Sephrarose, and hydroxylapatite column chromatography were used to purify the preparation. As a final step on a small scale, preparative sodium dodecyl sulfate (SDS) – polyacrylamide gel electrophoresis was used. The purified DNA polymerase exhibited a molecular weight of 85 000, as determined by both SDS–polyacrylamide gel electrophoresis and size-exclusion chromatography. Its pH optimum was in the range pH 7.5–8. When assayed over the temperature range 30–80 °C, the maximum activity in a 30-min assay was at 80 °C. The enzyme was moderately thermostable and exhibited half-lives of 3 min at 95 °C and 60 min at 50 °C in the absence of substrate. Several additives such as Triton X-100 enhanced thermostability. During storage at 4 °C and −70 °C, the stability of the enzyme was improved by the addition of gelatin.Key words: DNA polymerase, thermostable enzyme, Thermotoga.
Biosynthesis of phosphatidic acid by glycerophosphate acyltransferases in rat liver mitochondria and microsomes
Authors: Mok Amy Y. P. , McMurray William C.
Published: December 2009

The acyltransferases that catalyze the synthesis of phosphatidic acid from labelled sn-[14C]glycero-3-phosphate and fatty acyl carnitine or coenzyme A derivatives have been shown to be present in both isolated mitochondria and microsomes from rat liver. The major reaction product was phosphatidic acid in both subcellular fractions. A small quantity of lysophosphatidic acid and neutral lipids were produced as by-products. Divalent cations had significant effects on both mitochondrial and microsomal fractions in stimulating acylation using palmitoyl CoA, but not when palmitoyl carnitine was used as the acyl donor. Palmitoyl CoA and palmitoyl carnitine could be used for acylation by both mitochondria and microsomes. Mitochondria were more permeable to palmitoyl carnitine and readily used it as the substrate for acylation. On the other hand, microsomes yielded a better rate with palmitoyl CoA and the rate of acylation from palmitoyl carnitine in microsomes was correlated with the degree of mitochondrial contamination. The enzymes were partially purified from Triton X-100 extracts of subcellular fractions. Based on the differences of substrate utilization, products formed, divalent cation effects, molecular weights, and polarity, the mitochondrial and microsomal acyltransferases appeared to be different enzymes.Key words: glycerophosphate, acyltransferase, mitochondria, microsomes, phosphatidic acid.
Effect of heat shock on growth and division of Stylonychia mytilus
Authors: Kaul Sunil C.
Published: December 2009

Stylonychia mytilus cells grown at 23 °C exhibit an immediate arrest at G1 and S stages in the cell cycle when subjected to a heat shock of 1 h at 35 °C. The duration of arrest was seen to be dependent on the stage at which heat shock was given. It varied from 3 to 7 h and was synchronously accompanied by the delay in the completion of cell cycle. G2 and the early dividing stage D1 were found to be even more sensitive to heat shock than G1 and S phases. Cells divide normally when heat shock was given at the late dividing stage D2. However, the G1 stage of progeny cells was prolonged to 30 h from normal 5.5 h. These observations have been compiled from the cytological studies of normal and heat-shocked Stylonychia mytilus cells at different stages of cell cycle.Key words: Stylonychia mytilus, heat shock, cell cycle, division delay.
Effects of Ca2+ and Mg2+ on ATP-dependent 45Ca2+ influx in A-431 human epidermoidal carcinoma cells
Authors: Sugita Kenji , Hosoi Kazuo , Shioda Yoshimi , Ueha Takao
Published: December 2009

Upon stimulation with 10−6–10−3 M ATP, A-431 human epidermoidal carcinoma cells incorporated radioactive calcium from their medium in a temperature-dependent manner. The rate of incorporation of 45Ca2+ was rapid for the initial 5 min, but decreased immediately thereafter. The preincubation of cells for 2 h in medium depleted of both Ca2+ and Mg2+ abolished the ATP-dependent 45Ca2+ incorporation, irrespective of whether or not the subsequent incubation medium contained Mg2+ ions. ATP-dependent 45Ca2+ incorporation could be restored by a second preincubation (1 h) in medium containing 1 mM Mg2+, but no Ca2+. The Mg2+ ions in the second preincubation medium could be replaced by Ca2+, Co2+, or Cu2+ for restoration of such activity. Elevation of inositol trisphosphate (InsP3) was observed in cells depleted of either Ca2+ or Mg2+, but not in cells depleted of both ions. A parallel effect was observed in changes in [Ca2+]i. Since the concentration of cytosolic calcium ions does not change by incubation of cells in medium depleted of and (or) restored with calcium ions, we conclude that either calcium or magnesium ions associated with some cellular component(s) are responsible for production of InsP3, which then supposedly mobilizes Ca2+ and provokes 45Ca2+ influx.Key words: intracellular calcium ion, inositol trisphosphate, calcium influx.
Production of monoclonal antibodies against the N-terminal glycopeptide of porcine pro-opiomelanocortin: their use for solid-phase radioimmunoassay, western blotting, and immunogold cytochemistry
Authors: Chevrier Daniel , Lemieux Edith , Fyfe Mireille , Labonté N. , Zollinger Max , Bennett Hugh P. J. , Crine Philippe
Published: December 2009

We have prepared two monoclonal antibodies for the N-terminal glycopeptide of pro-opiomelanocortin 1–77 (N-POMC(1–77)) purified from porcine pituitaries. Antibody 1–244 recognizes an epitope located within the γ3-melanotropin (γ3-MSH or POMC(51–77)) sequence, whereas antibody 2–197 binds specifically to a determinant in the 1–49 region of N-POMC. These monoclonal antibodies were used to construct a two-site solid-phase radioimmunoassay that can detect as little as 50 pg of N-POMC(1–77). The assay is linear between 0.5 and 5 ng of porcine peptide and recognizes equally well the homologous peptides purified from human and bovine pituitaries. The assay has been used to analyze reversed-phase high pressure liquid chromatography fractions of crude bovine pituitary extracts and detected a peptide with chromatographic properties identical to those of N-POMC(1–77). When used to stain immunoblots of bovine intermediate pituitary extracts, both the 2–197 and 1–244 antibodies could recognize a major peptide comigrating with purified N-POMC(1–77). In addition, antibody 2–197 also detected a peptide with a mobility similar to that of standard N-POMC(1–49). When used in conjunction with a second anti-mouse antibody coupled to colloidal gold particles, antibody 2–197 stained N-POMC immunoreactive material located in granules in thin sections of pituitary.Key words: monoclonal antibodies, γ-melanotropin, pituitary hormones.
RNA transcription and translation in the hearts of normal and cardiomyopathic Syrian hamsters
Authors: McCully J. D. , Mably J. D. , Sole M. J. , Liew C. C.
Published: December 2009

The cardiomyopathic Syrian hamster has an autosomal recessive defect that results in the development of an early onset cardiac myopathy leading to cardiac dysfunction and, eventually, complete heart failure. To assess the regulatory mechanisms modulating gene expression in the normal and myopathic myocardium, we investigated both RNA transcription and translation. Our results indicated that the incorporation of [3H]UMP into myocardial cell nuclear RNA decreased 10-fold from 7 to 210 days of age in the normal Syrian hamster. The incorporation of [3H]UMP was approximately 50% lower in the cardiomyopathic as compared with the normal Syrian hamster. RNA translation, as assessed by rabbit reticulocyte lysate in vitro translation, indicated that a coordinated 50% decrease in RNA translation occurred in the normal Syrian hamster from 7 to 210 days of age. A further reduction of 20% in translation was found in cardiomyopathic Syrian hamster ventricular RNA translation as compared with matched random bred control groups. Two-dimensional polyacrylamide gel analysis of cell-free translated protein products demonstrated two myocardial peptides that were found to be consistently altered when the normal and cardiomyopathic Syrian hamsters were compared. These results indicate that transcription and translation decrease with age and that these processes are further downregulated, in an additive manner, with the genesis of the disease process.Key words: cardiomyopathy, ribonucleic acid, transcription, translation.
Immunodetection of thiol proteinase levels in various populations of Artemia cysts and during development
Authors: Lu J. , Warner A. H.
Published: December 2009

An immunodetection assay on Western blots has been used to determine the thiol proteinase content and composition in cysts from 12 populations of the brine shrimp Artemia. Our results showed no differences in the subunit composition of the thiol proteinase among cysts from eight bisexual strains and four parthenogenic strains, and confirmed an earlier finding that the proteinase is composed of two subunits of 25.9 and 31.5 kilodaltons. In contrast, we found that Artemia cysts from parthenogenic strains contain 17.1 ng/cyst of the thiol proteinase, while cysts from bisexual strains contain 8.2 ng/cyst of the thiol proteinase. Also, there was a good linear correlation (r = 0.863; p < 0.001) between the thiol proteinase content and cyst mass. Embryo fractionation experiments showed that 82% of the thiol proteinase was in the cytosol, while 14 and 4%, respectively, were in the nuclei/yolk platelets and mitochondria/lysosome fractions. Measurements of the thiol proteinase content of developing Artemia embryos showed that the proteinase content was relatively constant during early development, suggesting that the activity of the thiol proteinase gene(s) may be constitutive and not developmentally regulated in Artemia embryos.Key words: Artemia, proteinase, development, cathepsin B, Western blotting.
Characterization of ATP-dependent Ca2+ transport in the basolateral membrane vesicles from proximal and distal tubules of the rabbit kidney
Authors: Ramachandran Chidambaram , Chan Meanthan , Brunette Michèle G.
Published: December 2009

Basolateral membrane vesicles were prepared from purified proximal and distal tubules of the rabbit kidney. The properties of the ATP-dependent Ca2+ transport were investigated. In both membranes, there was a high affinity, ATP-dependent Ca2+ transport system (Km = 0.1 μM). The optimal concentration of Mg2+ was 0.5 mM and the optimal concentration of ATP was 1 mM. The nucleotide specificity and pH dependence of the Ca2+ transport in both membranes were similar. In basolateral membrane vesicles, calmodulin had no effect on Ca2+ transport. However, in basolateral membrane vesicles depleted of calmodulin, exogeneous calmodulin increased the Ca2+ transport by increasing maximal velocity. There were no major differences in the properties of the ATP-dependent Ca2+ transport system in these two membranes. These findings are discussed in relation to why parathyroid hormone differentially modulates Ca2+ transport in these two segments of the nephron.Key words: Ca2+ transport, ATP-dependent, kidney, proximal tubule, distal tubule, basolateral membrane.
The puh structural gene coding for the H subunit of the Rhodospirillum rubrum photoreaction center
Authors: Bérard Jacques , Gingras Gabriel
Published: December 2009

The Rhodospirillum rubrum structural gene puh, coding for the photoreaction center H polypeptide, and three other putative genes that surround puh were cloned and sequenced. The deduced 257 amino acid H polypeptide has a molecular weight of 27 909, in close agreement with polyacrylamide gel electrophoresis determination. Hydropathy plots predict a single hydrophobic α helix. The H polypeptide of Rhodospirillum rubrum shares only 23% of its residues with all three of the H polypeptides from Rhodopseudomonas viridis, Rhodobacter capsulatus, and Rhodobacter sphaeroides. Despite this apparent low degree of similarity, statistical analysis leaves no doubt about their close relatedness. Interspecies evolutionary distance, assessed by this analysis, confirms the closeness of the two Rhodobacter species, Rhodospirillum rubrum and Rhodopseudomonas viridis being approximately equidistant from them. Three regions of the H polypeptide are highly conserved in all four species. They correspond to known contact points of H with the complex of the other two (L and M) subunits on the cytoplasmic side of the membrane. A glutamic acid residue (H polypeptide residue 177), conserved in the other bacteria and suggested to be involved in the binding of secondary quinone QB, is replaced by serine in Rhodospirillum rubrum. The open reading frames G115, I2372, and I3087 are predicted to, respectively, encode polypeptides of 480, 224, and 155 residues coiled in 10, 2, and 1 transmembrane helices. Open reading frame G115 shares 56% identical residues with F1696, a sequence similarly arranged in the genome of Rhodobacter capsulatus. The gene product of ORF 13087 is predicted to share highly similar sequences with nitrogenase reductase (encoded by nifH) of 11 different bacterial species and is suggested to have a regulatory function.Key words: gene puh, DNA sequence, codon usage, evolution.
The interaction between halogenated anaesthetics and bacteriorhodopsin in purple membranes as examined by intrinsic ultraviolet fluorescence
Authors: Lee Ki-Hwan , McIntosh Alan R. , Boucher François
Published: December 2009

In the presence of halogenated general anaesthetics such as enflurane and halothane, the spectral properties of the bacteriorhodopsin pigment contained in the purple membranes of Halobacterium halobium are strongly modified. It is reversibly transformed into a red-coloured species absorbing maximally at 480 nm, at the expense of its characteristic 570-nm absorption band. The ultraviolet fluorescence of bacteriorhodopsin has been used to probe the structural modifications that are reflected by this spectral change. Our results show that they are very small and do not perturb the energy transfer dynamics which take place between the aromatic amino acid residues and the retinyl chromophore. The fluorescence properties of anaesthetic-treated bacteriorhodopsin are dominated by the quenching properties of the halogenated hydrocarbon, which are obvious even at anaesthetic concentrations under those needed to induce a spectral change in the bacteriorhodopsin chromophore. This does not rule out direct interaction between anaesthetics and bacteriorhodopsin, but it indicates that the chromophoric site might well not be their primary target.Key words: purple membranes, bacteriorhodopsin, anaesthetics, fluorescence, quenching.
Fractionation of renal brush border membrane proteins with Triton X-114 phase partitioning
Authors: Vachon Vincent , Pouliot Jean-François , Laprade Raynald , Béliveau Richard
Published: December 2009

Analysis of brush border membrane proteins by gel electrophoresis has revealed a complex polypeptide composition. We have investigated the use of Triton X-114 phase partitioning to fractionate such proteins on the basis of their degree of hydrophobicity. Each of the fractions was composed of a complex but distinct set of proteins. Most proteins were solubilized by Triton X-114 and partitioned into the detergent-poor fraction. Trehalase, γ-glutamyl transpeptidase, and leucine aminopeptidase were well solubilized (> 80%) and enriched 5.1-, 3.9-, and 2.5-fold in the detergent-rich fraction. In contrast, alkaline phosphatase and 5′-nucleotidase were poorly solubilized. The specific activities of these enzymes were increased 2.7- and 2.3-fold in the insoluble protein fraction. Maltase was almost completely solubilized and partitioned into the detergent-poor fraction with a small enrichment factor (1.3). These results suggest that Triton X-114 phase partitioning could be useful as a first step in the purification of many brush border membrane proteins.Key words: Triton X-114, phase partitioning, brush border membrane, kidney, proteins.
Purification and characterization of purine nucleoside phosphorylase from developing embryos of Hyalomma dromedarii
Authors: Kamel Mamdouh Y. , Fahmy Afaf S. , Ghazy Abdel H. , Mohamed Magda A.
Published: December 2009

Purine nucleoside phosphorylase from Hyalomma dromedarii, the camel tick, was purified to apparent homogeneity. A molecular weight of 56 000 – 58 000 was estimated for both the native and denatured enzyme, suggesting that the enzyme is monomeric. Unlike purine nucleoside phosphorylase preparations from other tissues, the H. dromedarii enzyme was unstable in the presence of β-mercaptoethanol. The enzyme had a sharp pH optimum at pH 6.5. It catalyzed the phosphorolysis and arsenolysis of ribo- and deoxyribo-nucleosides of hypoxanthine and guanine, but not of adenine or pyrimidine nucleosides. The Km values of the enzyme at the optimal pH for inosine, deoxyinosine, guanosine, and deoxyguanosine were 0.31, 0.67, 0.55, and 0.33 mM, respectively. Inactivation and kinetic studies suggested that histidine and cysteine residues were essential for activity. The pKa values determined for catalytic ionizable groups were 6–7 and 8–9. The enzyme was completely inactivated by thiol reagents and reactivated by excess β-mercaptoethanol. The enzyme was also susceptible to pH-dependent photooxidation in the presence of methylene blue, implicating histidine. Initial velocity studies showed an intersecting pattern of double-reciprocal plots of the data, consistent with a sequential mechanism.Key words: Acarina, Hyalomma dromedarii, purine nucleoside phosphorylase, kinetics, active site, catalytic mechanism.
Glucose and caffeine regulation of liver glycogen phosphorylase activity in the freeze-tolerant wood frog Rana sylvatica
Authors: Risman Carey A. , David Emina S. , Storey Kenneth B. , Crerar Michael M.
Published: December 2009

We have examined the effect of glucose and caffeine inhibition on the activity of liver glycogen phosphorylase a from the freeze-tolerant frog Rana sylvatica. Kinetic studies indicate that this enzyme exhibits similar sensitivity to glucose inhibition (glucose dissociation constant = 12.5 mM) as the mammalian enzyme. Little inhibition (< 25%) was observed at normal glucose concentrations (1–5 mM), while significant inhibition (60–95%) occurred at glucose concentrations (50–500 mM) present in freezing-exposed animals. These results favour the hypothesis that in the normal state glucose regulates phosphorylase activity primarily through the promotion of dephosphorylation of phosphorylase a, whereas during freezing regulation is achieved through phosphorylase a inactivation. The caffeine dissociation constant (0.93 mM) and the degree of synergism between caffeine and glucose (interaction factor, α = 0.14) were also similar to that observed for the mammalian enzyme. Hence, if a caffeine-like ligand exists in vivo, it must be in low enough amounts during freezing to allow sufficient phosphorylase a activity for high glucose production.Key words: glycogen phosphorylase, glucose regulation, caffeine inhibition, freeze tolerance, cryoprotection.
Insulin and transferrin restore important cellular functions of human fetal kidney in serum-free organ culture
Authors: Brière Normand , Ferrari Joseph , Chailler Pierre
Published: December 2009

A model previously developed in our laboratory to culture human fetal kidneys in serum-free chemically defined medium was used to evaluate the direct influence of potential regulators on nephrogenesis. The aim of the present work was to verify the effects of insulin and transferrin, two hormones considered as essential in other serum-free culture systems. Explants of renal cortex from human fetuses (15–21 weeks) were cultured for 2 and 5 days in serum-free Leibovitz's L-15 medium (37 °C, 95% air – 5% CO2). The addition of transferrin (5 μg/mL) had no effect, but insulin (30, 60, and 125 mU/mL) increased DNA and protein syntheses in a dose-dependent manner. The influence of insulin (125 mU/mL) was potentiated by the addition of transferrin and the combination of the two stimulated DNA synthesis by threefold on day 2 when compared with controls and by sixfold on day 5 of culture. After 5 days, synthesis was restored to values observed at day 0. Transferrin did not modify the insulin effect on protein synthesis, since the latter was already maximally stimulated as early as day 2 of culture and at levels well above that of uncultured explants (day 0). The activities of four hydrolases considered as markers of brush border differentiation were not importantly changed by any of the hormones, supplemented alone or in combination. The results indicate that proliferation rather than differentiation is the parameter mostly influenced by these two hormones. The combination of insulin plus transferrin restores cellular functions of human fetal kidney explants cultured in serum-free medium. The potentiation of insulin influence possibly results from an increase in the number of transferrin receptors. The above additions optimize the present culture system and establish its usefulness as a valuable tool to study the direct influence of different effectors involved in human metanephrogenesis.Key words: insulin, transferrin, culture, nephrogenesis.
The effect of dimethylsulfoxide on adenine nucleotide binding and ATP synthesis by beef-heart mitochondrial F1 ATPase
Authors: Beharry Seelochan , Bragg Philip D.
Published: December 2009

Dimethylsulfoxide (Me2SO; 30%, v/v) promotes the formation of ATP from ADP and phosphate catalyzed by soluble mitochondrial F1 ATPase. The effects of this solvent on the adenine nucleotide binding properties of beef-heart mitochondrial F1 ATPase were examined. The ATP analog adenylyl-5′-imidodiphosphate bound to F1 at 1.9 and 1.0 sites in aqueous and Me2SO systems, respectively, with a KD value of 2.2 μM. Lower affinity sites were present also. Binding of ATP or adenylyl-5′ -imidodiphosphate at levels near equimolar with the enzyme occurred to a greater extent in the absence of Me2SO. Addition of ATP to the nucleotide-loaded enzyme resulted in exchange of about one-half of the bound ATP. This occurred only in an entirely aqueous medium. ATP bound in Me2SO medium was not released by exogenous ATP. Comparison of the effect of different concentrations of Me2SO on ADP binding to F1 and ATP synthesis by the enzyme showed that binding of ADP was diminished by concentrations of Me2SO lower than those required to support ATP synthesis. However, one site could still be filled by ADP at concentrations of Me2SO optimal for ATP synthesis. This site is probably a noncatalytic site, since the nucleotide bound there was not converted to ATP in 30% Me2SO. The ATP synthesized by F1 in Me2SO originated from endogenous bound ADP. We conclude that 30% Me2SO affects the adenine nucleotide binding properties of the enzyme. The role of this in the promotion of the formation of ATP from ADP and phosphate is discussed.Key words: F1 ATPase, ATP synthesis, dimethylsulfoxide, adenine nucleotide binding, mitochondrial ATPase.
Analysis of RNA for transcripts for catalase and SP71 in rat hearts after in vivo hyperthermia
Authors: Currie R. William , Tanguay Robert M.
Published: December 2009

Hyperthermic stress induces synthesis of the major inducible (heat) stress protein (SP71) in all rat tissues. In addition, there is an increase in catalase activity in hearts at 24 and 48 h after the induction of the heat shock response. To more precisely define some of the molecular aspects of the induction of the heat shock response in hearts, we examined mRNA levels for the catalase, SP71 and HSP27. RNA was isolated from control hearts and at various time periods (0–24 h) of recovery after brief hyperthermic treatment and was analyzed by Northern blot analysis using as probes cDNA sequences for rat liver catalase, human HSP70 (inducible), and human HSP27. There was no detectable change in mRNA for catalase after heat shock or during recovery. Hyperthermic stress has no apparent effect on the regulation of transcription of mRNA coding for catalase, indicating that the increase in catalase activity is either translationally or post-translationally regulated. The human HSP70 cDNA did not hybridize to control heart RNA, but did hybridize to SP71 transcripts at 0, 1.5, and 3 h post heat shock. The mRNA level for SP71 peaked at 1.5 h, was reduced at 3 h, and became almost undetectable at 6 h post heat shock. Similarly, the human HSP27 cDNA did not hybridize to control heart RNA, but did hybridize to transcripts for HSP27 at 0, 1.5, 3, and up to 15 h post heat shock. Maximal signal for HSP27 was at 3 h post heat shock and was sharply reduced at 6 h post heat shock. The accumulation of transcripts for SP71 and HSP27 after hyperthermic stress is rapid, and degradation of the transcripts is almost complete by 6 h post heat shock.Key words: heat shock proteins, hyperthermia, catalase, heart, RNA.
Gene expression during cold and heat shock in wheat
Authors: Danyluk Jean , Rassart Eric , Sarhan Fathey
Published: December 2009

Translatable messenger RNAs expression was compared in cold- and heat-stressed winter wheat (Triticum aestivum L. 'Fredrick' and 'Norstar') and spring wheat (T. aestivum L. 'Glenlea'). Polyadenylated RNA isolated from the crown and leaf tissues was translated in a wheat germ cell free system and the acidic and basic in vitro products were resolved by two-dimensional SDS–PAGE and autoradiography. The results showed that low temperature stress rapidly induced two groups of mRNAs. The first group was transient in nature and consists of 18 mRNAs that reached their highest levels of induction after 24 h of low temperature exposure and then decreased to undetectable levels. The second group consists of 53 mRNAs that were also induced or increased rapidly, but maintained their levels of expression during the 4 weeks required to induce freezing tolerance. Among those, at least 34 were expressed at higher levels in the freezing tolerant winter wheat compared with the less tolerant spring wheat. This suggests a possible relation between the expression of these mRNAs and the capacity of each genotype to develop freezing tolerance. In the case of heat shock, 50 mRNAs were induced or increased after 3 h at 40 °C. Among these, the expression of only six mRNAs was altered in a similar manner in the three genotypes by both treatments. The remaining mRNAs code for typical heat shock proteins which are different from those induced by low temperature. None of these mRNAs has been associated with the development of freezing tolerance. These results suggest that heat and cold stress are controlled by different genetic systems.Key words: wheat, mRNAs, proteins, low temperature, heat stress.
Qualitative changes in the fluorescence spectra of intact pea leaves after photoinhibition
Authors: Gruszecki Wiesław I. , Veeranjaneyulu Konka , Leblanc Roger M.
Published: December 2009

In high light (1400 W m−2) treated, intact pea leaves, a decrease in the ratio of fluorescence emission at 685 to 730 nm and an increase in fluorescence intensity between 500 and 600 nm were observed. Furthermore, photoacoustically monitored heat emission increased slightly, and O2 evolution decreased significantly. These findings are interpreted as effects of a photoprotective mechanism separating the carotenoid pool from the chlorophylls. This is supported by fluorescence excitation measurements and the results of a study on the reversibility of the process.Key words: chlorophyll fluorescence, carotenoid fluorescence, photoinhibition, photosynthesis, energy transfer.
Expression of growth hormone, growth hormone releasing hormone, and somatostatin genes is unperturbed in the streptozotocin-induced diabetic rat
Authors: Lee Jiann-Gwu , Bird R. Curtis , Oliver Elizabeth H. , Sartin James L.
Published: December 2009

The effects of streptozotocin diabetes on the level of growth hormone, growth hormone releasing hormone, and somatostatin mRNA was measured in control rats, in diabetic rats maintained on insulin, and in diabetic rats in which insulin had been withheld for 3 days. Total cytoplasmic RNA samples were prepared from the pituitary and hypothalamic tissues of each animal and analyzed by dot blot or Northern blot hybridization. No significant difference was observed between control and insulin-treated groups with regard to body weight or plasma glucose concentration. The insulin withdrawal group had significantly higher plasma glucose concentrations and lower body weights, confirming diabetic status. There was no significant difference in the level of growth hormone, growth hormone releasing hormone, and somatostatin mRNA among any of the three groups however. We conclude that alterations in the regulation of circulating growth hormone in the streptozotocin-induced diabetic rat, removed from insulin treatment for 3 days, did not occur at the transcriptional or RNA processing level. This conclusion extends to hypothalamic growth hormone releasing hormone, and somatostatin gene expression as well. Regulatory changes in growth hormone level previously noted during insulin withdrawal in the streptozotocin-induced diabetic rat could be the result of post-transcriptional processes operating at the level of hormone synthesis or release.Key words: growth hormone, growth hormone releasing hormone, somatostatin, insulin, streptozotocin-induced diabetes, mRNA.
An experimental test of a model for repeated Ca2+ spikes in osteoblastic cells
Authors: Ferrier Jack , Kesthely Angela , Lagan Eva , Richter Conrad
Published: December 2009

A model for cytosolic Ca2+ spikes is presented that incorporates continual influx of Ca2+, uptake into an intracellular compartment, and Ca2+-induced Ca2+ release from the compartment. Two versions are used. In one, release is controlled by explicit thresholds, while in the other, release is a continuous function of cytosolic and compartmental [Ca2+]. Some model predictions are as follows. Starting with low Ca2+ influx and no spikes: (1) induction of spiking when Ca2+ influx is increased. Starting with spikes: (2) increase in magnitude and decrease in frequency when influx is reduced; (3) inhibition of spiking if influx is greatly reduced; (4) decrease in the root-mean-square value when influx is increased; and (5) elimination of spiking if influx is greatly increased. Since there is good evidence that hyperpolarizing spikes reflect cytosolic Ca2+ spikes, we used electrophysiological measurements to test the model. Each model prediction was confirmed by experiments in which Ca2+ influx was manipulated. However, the original spike activity tended to return within 5–30 min, indicating a cellular resetting process.Key words: calcium, electrophysiology, mathematical modelling.
Characterization of plasminogen binding to human capillary and arterial endothelial cells
Authors: Ganz Peter R. , Dupuis Denis , Dudani Anil K. , Hashemi Sofia
Published: December 2009

Phenotypic diversity of endothelial cells that line the various vascular spaces has been well established. However, it is not known if biochemical differences also exist, particularly in the numbers of receptors for plasma proteins. Equilibrium binding techniques were used to assess potential differences in the binding of 125I-labelled plasminogen to cultured human umbilical arterial endothelial cells and capillary endothelium, as compared with umbilical venous cells. The kinetic behaviour of plasminogen binding to all three types of cells was similar, with optimal binding occurring between 20 and 30 min of incubation. Binding of plasminogen to arterial, capillary, and venous cells was concentration dependent and reversible upon addition to excess unlabelled plasminogen. Scatchard analyses showed that artery, capillary, and venous endothelial cells all possess low affinity sites for plasminogen with Kd values of 0.30 ± 0.07, 0.40 ± 0.06, and 0.40 ± 0.08 μM, respectively. Vein cells also possess an additional higher affinity binding site with a Kd of 0.07 ± 0.01 μM, exhibiting a 6-fold greater affinity for plasminogen than the lower affinity sites on capillary and arterial endothelial cells. Assuming a stoichiometry of 1:1 for binding, the data indicate that arterial and capillary endothelial cells contain approximately 4.2 (± 0.9) × 106 and 4.1 (± 0.6) × 106 plasminogen receptors per cell. Venous cells contain both low and high density binding sites with 6.2 (± 0.8) × 106 and 12.4 (± 2.4) × 106 sites per endothelial cell. The presence of a higher affinity site on vein cells, but not on artery or capillary cells, may signal functional differences relating to fibrinolytic activity on the surface of these cells. Ligand blotting experiments, in which labelled plasminogen was adsorbed to polypeptides recovered from endothelial cell lysates, identified polypeptides of 46, 45, and 37 kDa, which may constitute the plasminogen-binding sites–receptors on endothelial cells.Key words: plasminogen, endothelial cells, receptors, fibrinolysis.
In vitro formation of retinoic acid from retinal in rat liver
Authors: Hupert Jordan , Mobarhan Sohrab , Layden Thomas J. , Papa Vincent M. , Lucchesi Deborah J.
Published: December 2009

Enzymatic conversion of retinal to retinoic acid in rat liver cytosol was detected using a rapid and sensitive assay based on high pressure liquid chromatography (HPLC). This retinal oxidase assay system did not require extraction steps or any other manipulation of the sample mixture once the sample vial was sealed for incubation. The product (retinoic acid) and the reactant (retinal) were separated by HPLC in 14.0 min with a sensitivity of 15 and 40 pmol per injection for retinoic acid and retinal, respectively. Enzymatic activity was observed to be linear with protein concentration (0–2.4 mg/mL) and time (0–30 min) and displayed a broad pH maximum of 7.7–9.7. The enzyme exhibited Michaelis–Menten single-substrate kinetics with an apparent Km of 0.25 mM. The average specific activity in nine normal rats was 35.6 ± 3.3 nmol retinoic acid formed/h per mg protein. Incubation of the enzyme with zinc did not affect the rate of retinoic acid synthesis. Dithiothreitol inhibited the reaction. Both NAD and NADH stimulated retinoic acid formation. Formation of retinol was also observed when these pyridine nucleotides were added to the reaction mixture, indicating the presence of retinal reductase activity. The results of kinetic studies suggest that NADH may act indirectly to stimulate retinoic acid formation.Key words: retinal oxidase, retinoic acid, retinal, retinol, liver.
CPT-cAMP and okadaic acid enhance phosphatidylcholine catabolism in choline-deficient rat hepatocytes
Authors: Hatch Grant M. , Vance Dennis E.
Published: December 2009

The effect of CPT-cAMP and okadaic acid on phosphatidylcholine catabolism in suspension cultures of choline-deficient rat hepatocytes was investigated. Choline-deficient hepatocytes were pulse-labeled for 30 min with [methyl-3H]choline and subsequently chased for up to 60 min with choline in the absence or presence of 0.5 mM CPT-cAMP or 0.5 μM okadaic acid. Radioactivity in phosphatidylcholine and lysophosphatidylcholine were unchanged during the chase. However, the radioactivity incorporated into glycerophosphocholine was significantly increased (P < 0.05) 59 and 77% after 60 min of chase in hepatocytes incubated with either okadaic acid or CPT-cAMP, respectively. Incubation of choline-deficient hepatocytes with both okadaic acid and CPT-cAMP produced an additive effect on radioactivity incorporated ino glycerophosphocholine. Crude mitochondrial, microsomal, and cytosolic phospholipase–lysophospholipase activities, assayed in the presence of exogenously labeled phosphatidylcholine, were unchanged in both CPT-cAMP and okadaic acid treated hepatocytes compared with control. Phospholipase–lysophospholipase activity, assayed with endogenously labeled phosphatidylcholine, was increased 28 and 47% (P < 0.05) in the crude mitochondrial fraction of hepatocytes treated with either okadaic acid or CPT-cAMP, respectively, compared with the control. Incubation of choline-deficient hepatocytes, labeled with L-[methyl-3H]methionine, with CPT-cAMP or okadaic acid caused a 31 and 20% increase (P < 0.05) in the radioactivity incorporated into glycerophosphocholine, respectively, compared with the control. We postulate that phosphatidylcholine catabolism in choline-deficient hepatocytes may be regulated by a phosphorylation-dephosphorylation mechanism mediated through cAMP-dependent protein kinase and phosphoprotein phosphatase activities.Key words: phosphatidylcholine catabolism, choline deficiency, okadaic acid, CPT-cAMP.
Isolation, ultrastructure, and partial characterization of collagen from the perineurium of the Florida lobster, Panulirus argus
Authors: Baerwald Roy J. , Williamson Lura C. , Stevens E. , Rike C. , Trabanino S. , Carlton J.
Published: December 2009

Highly concentrated extracellular filaments in the perineurium of the Florida spiny lobster, Panulirus argus, were isolated using ultracentrifugation and linear sucrose gradients. The pellet obtained was highly enriched for the filaments as observed by transmission electron microscopy. Fibril diameter and axial periodicity measurements were obtained from filaments positively and negatively stained with uranyl acetate. A period between 14.0 and 25.0 nm and an average fibril diameter of 15.0 nm were observed. The filaments proved resistant to solubilization by most conventional agents and by several collagenases. NaOH (0.1 M at 100 °C) safely dissolved the filaments for measurements of protein content by the Lowry method and carbohydrate content with anthrone reagent. These tests revealed a protein content of ≈ 84% and a high carbohydrate content of ≈ 15%. Polyacrylamide electrophoresis of an acid-pepsin filament extract revealed a highly concentrated band (approximately 100 000) corresponding to the α-1 and α-2 bands of vertebrate type I collagen. Wide angle X-ray diffraction yielded meridional reflections that confirmed the filaments as collagen when compared with mammalian collagen X-ray diffraction. The amino acid composition was determined with a computer-assisted Beckman amino acid analyzer, which showed a glycine content of 279 residues/1000. Hydroxylysine and hydroxyproline were present in lower concentrations than expected.Key words: perineurium, lobster, collagen, extracellular matrix.
Purification and the effect of peptide N-glycosidase F on lysosomal membrane-bound glucocerebrosidase from human cultured fibroblasts
Authors: Choy Francis Y. M. , Woo Mary
Published: December 2009

Glucocerebrosidase was purified from human cultured dermal fibroblasts more than 2200-fold to apparent homogeneity using high performance Alkyl-Superose HR 5/5 hydrophobic interaction and Bio-Sil TSK-250 gel permeation column chromatography. Sodium dodecyl sulfate – polyacrylamide gel electrophoresis and protein staining of the catalytically active and concentrated enzyme fractions from the gel permeation columns revealed the presence of one band of Mr 64 000. The glucocerebrosidase preparation purified to homogeneity was digested with peptide N-glycosidase F that cleaves N-linked oligosaccharide structures from glycoproteins. The molecular weight of glucocerebrosidase after digestion with peptide N-glycosidase F was reduced to Mr 57 000, suggesting that the mature enzyme is a glycoprotein and that N-linked oligosaccharide constitutes a minimum of about 10% of the total molecular weight of the polypeptide. These findings are compatible with the hypothesis that glucocerebrosidase was initially synthesized as a precursor polypeptide which was subsequently glycosylated to become the mature enzyme.Key words: glucocerebrosidase, purification, deglycosylation, N-glycosidase F, fibroblasts.
Differential modulation of carbonic anhydrase (CA III) in slow- and fast-twitch skeletal muscles of rat following denervation and reinnervation
Authors: Milot J. , Frémont P. , Côté C. , Tremblay R. R.
Published: December 2009

Carbonic anhydrase III (CA III) is influenced by neuronal factors in skeletal muscles of the rat. CA III protein and its mRNA levels were assessed in slow- and fast-twitch muscles after short-term denervation by ligature of the sciatic nerve and reinnervation following removal of the sheath tightly fixed around the nerve. Significant elevations in the CA III mRNA content of fast-twitch muscles were recorded after denervation, but they were cancelled following spontaneous muscle reinnervation. No such variations were observed in the slow-twitch soleus muscle. CA III specific activity or cytosolic CA III protein content increased in both types of muscles after denervation, while a decrease was solely observed in the soleus after reinnervation. These results suggest that neuronal mediators may be responsible for up and down variations in CA III gene expression and (or) mRNA stability in slow- and fast-twitch muscles exposed to identical stimuli. Variations of the mRNA and the protein probably reflect, in a time-related manner, the well-programmed changes in fiber type of the muscles in the context of the denervation–reinnervation model.Key words: carbonic anhydrase III, skeletal muscles, denervation, reinnervation, rat.
Dependence on neutral salt concentration of the latency phase in the time course of hydrolysis of dimyristoylphosphatidylcholine liposomes by phospholipase A2
Authors: Fernández Marta S. , Mejía Ricardo , Zavala Eunice , Pacheco Fermín
Published: December 2009

The time course of the hydrolytic action of porcine pancreatic phospholipase A2 on sonicated dimyristoylphosphatidylcholine liposomes in the presence of variable NaCl concentrations has been studied at temperatures between 17 and 36 °C; at these temperatures liposomes are in the gel phase. At a NaCl concentration of 10 mM, the hydrolysis shows a small and constant lag period of 6–8 min at all temperatures within this range. As the temperature is raised into the liquid crystalline range, the latency phase lengthens monotonically so that at 36 °C it reaches 55 min. An increase in the NaCl concentration to 1 M makes the lag period longer at all temperatures studied, with the exception of the phase transition range (near 24 °C); within this temperature range, a small reduction in the lag time is observed. The increase in the length of the latency period at high salt concentrations may be due to screening of the negative surface charge generated by the nascent fatty acid which seems to be essential for the efficient interfacial binding of the enzyme. In the phase transition range of the lamellae, the unfavorable effect of high salt concentrations on the electrostatic binding of the enzyme appears to be overcome by another type of interaction. Recent findings raise the possibility that this interaction could be hydrophobic in nature.Key words: phospholipase A2, liposomes, hydrolysis, salt, latency phase.