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71.
Stimulation of vascular endothelial cells with agonists such as histamine and thrombin results in release of arachidonic acid from membrane lipids and subsequent eicosanoid synthesis. As shown previously, the agonist-stimulated deacylation is specific for arachidonate, eicosapentaenoate, and 5,8,11-eicosatrienoate. This study has utilized radiolabeled fatty acids differing in chain length and position of double bonds to further elucidate the fatty acyl specificity of agonist-stimulated deacylation. Replicate wells of confluent human umbilical vein endothelial cells were incubated with 14C-labeled fatty acids and then challenged with histamine, thrombin, or the calcium ionophore A23187. Comparison of the results obtained with isomeric eicosatetraenoic fatty acids with initial double bonds at carbons 4, 5, or 6 indicated that the deacylation induced by all three agonists exhibited marked specificity for the cis-5 double bond. Lack of stringent chain length specificity was indicated by agonist-stimulated release of 5,8,11,14- tetraenoic fatty acids with 18, 19, 20, and 21 carbons. Release of 5,8,14-[14C]eicosatrienoate was two-to threefold that of 5,11,14-[14C]eicosatrienoate, thus indicating that the cis-8 double bond may also contribute to the stringent recognition by the agonist-sensitive phospholipase. The present study has also demonstrated that histamine, thrombin, and A23187 do not stimulate release of docosahexaenoate from endothelial cells. 相似文献
72.
Evidence for the formation of covalent bonds between macromolecules in the domain of the wall of Candida albicans mycelial cells 总被引:9,自引:0,他引:9
V Elorza S Mormeneo F Garcia de la Cruz C Gimeno R Sentandreu 《Biochemical and biophysical research communications》1989,162(3):1118-1125
An O-glycosylated mannoprotein, after its incorporation into the wall, showed an increase in its molecular weight, due at least to its association with N-glycosidic sugar chain(s). This was shown by rendering the material soluble after partial degradation of the wall structure. At present it is unknown whether this phenomenon is due to an additional transglycosylation process or whether the partial degradation of the wall solubilizes a supramolecular structure formed between the original O-glycosylated protein which becomes linked either directly or indirectly through a protein to the N-sugar chain(s). 相似文献
73.
Summary The caudal spinal cord of the coho salmon was investigated by means of immunocytochemistry using antisera against serotonin, urotensin I, urotensin II, somatostatin and a urea-extract of bovine Reissner's fiber (AFRU). Populations of serotonin-immunoreactive (IR) neurons were found rostral and dorsal to the urophysis in close spatial association with caudal secretory neurons. Thick, smooth serotonin-IR processes extended toward the external surface of the spinal cord where they displayed conspicuous terminal dilatations. Thin, beaded serotonin-IR fibers appeared to innervate populations of caudal secretory and somatostatin-IR cerebrospinal fluid-contacting neurons. Most caudal neurosecretory cells displayed both urotensin I and urotensin II immunoreactivities; only a minority reacted exclusively with either urotensin I or urotensin II antisera. Urotensin II-IR and somatostatin-IR cerebrospinal fluid (CSF)-contacting neurons were found as an integral component of the central canal wall in the caudal spinal cord and filum terminale; their dendritic processes appeared to contact Reissner's fiber, which displayed a weak AFRU-immunoreactivity while inside the central canal, but became strongly reactive in the interior of the terminal ventricle as it formed the massa caudalis. The distribution of serotoninergic processes points to a regulatory role in the function of caudal secretory and CSF-contacting neurons and to a putative serotonin release into the subarachnoid space and/or meningeal vasculature. It is also suggested that the CSF-contacting neurons of the central canal may participate in a feedback mechanism controlling the secretory activity of the subcommissural organ.Supported by Grant A/1095-1 from the International Foundation for Science, Sweden, to C.Y.; Grant I/63-476 from Volkswagen-Stiftung to E.R.; and Grant S-85-39 from the Dirección de Investigaciones, Universidad Austral de Chile 相似文献
74.
S-Adenosylmethionine (SAM) synthetase of yeast and hyphal-phase cells of the dimorphic fungusCandida albicans was characterized by kinetic analysis and response to inhibitors. The enzyme from yeast-phase cells has a Km of 0.17 mM for methionine, 0.14 mM for ATP, and is inhibited (in vitro) by dimethyl-sulfoxide, methionine sulfone, and methionine sulfoxide. The hyphal-phase SAM synthetase has a Km of 0.06 mM for methionine, 0.02 mM for ATP, and its activity (in vitro) is enhanced by the substances that inhibit the yeast-phase enzyme. These data strongly suggest that isozymes of SAM synthetase are present inC. albicans and that they are possibly morphology specific. In vivo studies revealed that synthesis of the enzyme is repressed by the addition of methionine to the growth medium and that specific activity of the enzyme increases when intracellular SAM levels are lowered. In addition, it was shown that the increase in specific activity seen during yeast hypha morphogenesis and in yeast cells grown in a methionine-free medium involves de novo protein synthesis. 相似文献
75.
Cristina Sánchez-Roldán Antonio Heredia Victoriano Valpuesta Martin J. Bukovac 《Journal of Plant Growth Regulation》1990,9(1-3):171-174
The indole-3-acetic acid (IAA) content in peach pericarp (Prunus persica L. Batsch cv. Merry) was highest at early stage I of development (200 ng/g fresh wt), decreased to the lowest level during stage II, and rose again at stage III to 60–70 ng/g fresh wt. High activity of glutamine synthetase was found in the pericarp during stage I. The soluble peroxidase activity was highest in the meso- and exocarp at stage II, and isoenzymatic changes in this fraction corresponded to the transition from cationic isoenzymes, predominant at stage I, to anionic isoenzymes at stage III. The ionically bound peroxidase activity in these tissues was highest at stage I. The three developmental stages showed marked differences in auxin content and enzyme activities; for peroxidases these changes reflect a developmental expression pattern for the isoenzymes. 相似文献
76.
Bovine serum albumin, free of deoxyribonuclease activity, was obtained in our laboratory using ion-exchange chromatography followed by acetylation. Chromatography on four different resins (DEAE-52, P-11, hydroxylapatite and Q Sepharose fast-flow) was examined. Fractions from Q Sepharose chromatography, eluted with a linear gradient 0-1.0 M NaCl and subsequently acetylated, proved to be the most effective method for obtaining deoxyribonuclease-free bovine serum albumin. 相似文献
77.
Energetics of the hairpin to mismatched duplex transition of d(GCCGCAGC) on NaCl solution 总被引:1,自引:0,他引:1
A E Garcia G Gupta D M Soumpasis C S Tung 《Journal of biomolecular structure & dynamics》1990,8(1):173-186
We report Potential of Mean Force studies to describe the relative thermodynamic stabilities of d(GCCGCAGC) in a mismatched duplex and a hairpin monomer conformation in NaCl solution. The PMF calculations are combined with previous molecular mechanics and normal mode analysis in order to estimate the role of different components of the free energy in determining the relative stability of the duplex and hairpin structures. The high entropy associated with the loop region and the lack of minor groove phosphate-phosphate interactions in the hairpin compete against the gain in enthalpic contribution to the free energy due to base pairing in the mismatched duplex. The combined free energy calculations show that the hairpin is the most stable conformation at low salt and that a hairpin to duplex transition takes place at approximately 0.47 M NaCl. In addition, we studied the hairpin to partially stacked single helical conformation equilibrium at low salt. We found a small variation in transition temperature in salt concentration, delta Tm/delta log10(cs) approximately 2-3 degrees K/decade, in contrast to the duplex to hairpin or duplex to partially stacked single helix transition where the transition temperature exhibited marked dependence on salt concentration. This is in qualitative agreement with experimental data. Based on the Potential of Mean Force free energy calculation, the order of relative stability of the three-conformations studied varies with salt concentration. We observed the following orders of stability: stacked single helix greater than hairpin greater than duplex for cs less than 0.77 M NaCl; single helix greater than duplex greater than hairpin for 0.77 less than Cs less than 2.1 M; and duplex greater than hairpin greater than single strand for cs greater than 2.1 M. From the calculated PMF free energy curves in the NaCl concentration range, 0.012 less than cs less than 5.0 M, we can assign upper and lower bounds for the non-ionic differences in free energy between the duplex, hairpin, and stacked single helical states (at standard conditions: cs = 1.0 M, T = 25 degrees C, and 1 M oligomer concentration). We found that for delta G duplex single helix = G duplex - 2 x G single helix less than -7.38 Kcal/mol, the single helix is the least stable state. For the duplex-to-hairpin free energy difference in the range, -1.87 less than delta G duplex-hairpin less than 0.03 Kcal/mol, there will always be a salt-induced hairpin-to-duplex transition for 0.01 less than cs less than 1.6 M NaCl. If delta G duplex-hairpin less than -1.87, the duplex is always more stable than the hairpin; and for delta G duplex-hairpin greater than Kcal/mol, the hairpin state is always more stable than the duplex, for all salt concentrations. 相似文献
78.
79.
Biosynthesis of platelet-activating factor in glandular gastric mucosa. Evidence for the involvement of the ''de novo'' pathway and modulation by fatty acids. 总被引:1,自引:0,他引:1
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S Fernandez-Gallardo M A Gijon M C Garcia E Cano M Sanchez Crespo 《The Biochemical journal》1988,254(3):707-714
The biosynthesis of platelet-activating factor (PAF), a phospholipid autocoid with potent ulcerogenic properties that is produced in secretory exocrine glands by physiological secretagogues, was assessed in microsomal preparations of glandular gastric mucosa. For this purpose, 1-O-alkyl-2-lyso-sn-glycero-3-phosphocholine (lyso-PAF):acetyl-CoA acetyltransferase (EC 2.3.1.67); the enzymes of the 'de novo' pathway: 1-O-alkyl-2-lyso-sn-glycero-3-phosphate (alkyl-lyso-GP):acetyl-CoA acetyltransferase and 1-O-alkyl-2-acetyl-sn-glycerol (alkylacetyl-G):CDP-choline cholinephosphotransferase (EC 2.7.8.16); and some enzymes involved in the catabolism of PAF and lyso-PAF were assayed. Only the enzymes of the 'de novo' pathway and small amounts of PAF acetylhydrolase, phospholipase A2 and a lysophospholipase D acting on either lipids could be detected in the gastric preparations, whereas lyso-PAF:acetyl-CoA acetyltransferase activity was undetectable. The specific activity of alkyl-lyso-GP:acetyl-CoA acetyltransferase in the gastric mucosa was about one-tenth of that found in spleen microsomes and its apparent Km for acetyl-CoA was 454 microM compared with 277 microM in spleen microsomes. Glandular mucosa homogenates contained preformed PAF at a concentration of 2.7 +/- 0.7 ng equivalents of PAF (hexadecyl)/mg of protein. When gastric microsomes were incubated with micromolar concentrations of fatty acids (arachidonic, palmitic and oleic) prior to the assay of dithiothreitol (DTT)-insensitive cholinephosphotransferase, a dose-dependent reduction in the formation of PAF was observed, arachidonic acid being the most potent inhibitor, followed by linoleic acid (only tested on spleen microsomes) and oleic acid. By contrast, 1,2-diolein and phosphatidylcholine (dipalmitoyl) showed no or little effect. These results indicate that glandular gastric mucosa can produce PAF through the 'de novo' pathway, and that fatty acids, especially unsaturated, can reduce that synthesis by modulating the expression of DTT-insensitive cholinephosphotransferase. 相似文献
80.
Dr. Concepción Calvo Ana García de la Paz Victoria Bejar Emilia Quesada Alberto Ramos-Cormenzana 《Current microbiology》1988,17(1):49-53
Thirty-eight strains ofDeleya halophila species were examined for production of phage after mitomycin C induction. Thirty-two of them were able to inhibit growth of some other strains. Phage F9-11, isolated fromD. halophila strain F9-11, showed an isometric head and a noncontractile tail. The effects of salt concentrations variation on the stability and replication of this phage were established. Its replication was possible at a wide range of marine salt concentrations, from 2.5% to 15% (wt/vol). Stability seems to be influenced by osmolarity of medium rather than by NaCl level. The euryhaline character showed by F9-11 phage is evoked as an important factor for the survival of this phage in its environment. 相似文献