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991.
992.
The activities of NADPH and NADH oxidase were determined in homogenates of isolated pure parenchymal and nonparenchymal rat liver cells at neutral (7.4) and acid (5.5) pH. The NADPH oxidase at pH 7.4 is about equally active in parenchymal and nonparenchymal cells and in both cell types is rather insensitive to KCN (1 mm) inhibition. By lowering the pH to 5.5, the NADPH oxidase of the nonparenchymal cells is stimulated (twofold) while the activity in parenchymal cells is decreased. The NADH consumption at neutral pH in parenchymal cells is 75% inhibited by KCN, while this activity in nonparenchymal cells is relatively insensitive to KCN. The NADH oxidase in both parenchymal and nonparenchymal liver cells is less active when the pH is lowered from 7.4 to 5.5. The distribution of NAD(P)H oxidases between parenchymal and nonparenchymal liver cells and the effect of pH on their activities suggest that in the nonparenchymal cells, the NADPH oxidase might play a role in the synthesis of H2O2 within the phagocytic vacuole. A scheme is proposed which describes the metabolic events involved in H2O2 formation and catabolism of endo(phago)cytosed particles in nonparenchymal liver cells. 相似文献
993.
The phospholipid monolayer technique has been used to study the transfer activity of the phospholipid exchange protein from beef brain. In measuring the transfer between a monolayer consisting of equimolar amounts of phosphatidylcholine and phosphatidylinositol and liposomes consisting of 98 mol% phosphatidylcholine and 2 mol% phosphatidylinositol, the beef brain protein demonstrates an 8-fold higher transfer activity for phosphatidylinositol than for phosphatidylcholine. Under similar conditions the phosphatidylcholine exchange protein from beef liver showed a great preference for phosphatidylcholine. Phosphatidylcholine liposomes devoid of phosphatidylinositol still functioned as receptors of phosphatidylinositol when the beef brain exchange protein was present. This indicates that this protein can catalyse a net transfer of phosphatidylinopsitol. Binding of both phosphatidylinositol and phosphatidylcholine to the beef brain protein was shown. 相似文献
994.
From data obtained by differential scanning calorimetry phase diagrams were constructed, using a thermodynamically based fitting method. The following binary mixtures of phosphatidylcholines in water were studied: 14:0/ 14:0-glycerophosphocholine/16:0/16:0-glycerophosphocholine, 14:0/14:0-glycerophosphocholine /18:0/18:0-glycerophosphocholine, 12:0/12:0-glycerophosphocholine /16:0/16:0-glycerophosphocholine, 18:1t/18:1t-glycerophosphocholine /14:0/14:0-glycerophosphocholine and 18:1t/18:1t-glycerophosphocholine /16:0/16:0-glycerophosphocholine.A comparison is made of the present results with those obtained using probe techniques and the differences are discussed. 相似文献
995.
Summary Cell suspensions of the fresh-watersponge Ephydatia fluviatilis have been fractionated by means ofFicoll gradient centrifugation. Three fractions were isolated. The densest contains archeocyte-like cells only; the intermediate fraction is very rich in choanocytes, and the lightest is a mixture of cell types. Earch fraction shows specificaggregative properties and potentialities to reconstitute functional sponges.It appears that the sequence of reconstitution events can be selectively altered by certain disequilibria in the cell populationThese preliminary results constitute a first approach to the analysis ofcell type specificity in sponges. 相似文献
996.
997.
998.
Juan Ortín Concepción Martínez Lucía del Río Mercedes Dávila Cecilio López-Galíndez Nieves Villanueva Esteban Domingo 《Gene》1983,23(2):233-239
The complete genetic information contained in the influenza virus RNA segment 7 of the A/Bangkok/ (H3N2) strain has been cloned by in vitro synthesis of the complementary dsDNA and its insertion into plasmid pBR322. The nucleotide sequence of the viral RNA segment has been determined from the cDNA insert. It is 1027 nucleotides long, and contains two open reading frames, as shown for other influenza virus strains. When compared with the previously published sequence for the A/Udorn/72 (H3N2) strain, 15 nucleotide exchanges are observed, most of them silent mutations, and only two causing amino acid changes in each of the M1 and M2 protein sequences. 相似文献
999.
Voltage-dependent orientation of membrane proteins 总被引:1,自引:0,他引:1
R Blumenthal C Kempf J Van Renswoude J N Weinstein R D Klausner 《Journal of cellular biochemistry》1983,22(1):55-67
In order to study the influence of electrostatic forces on the disposition of proteins in membranes, we have examined the interaction of a receptor protein and of a membrane-active peptide with black lipid membranes. In the first study we show that the hepatic asialoglycoprotein receptor can insert spontaneously into lipid bilayers from the aqueous medium. Under the influence of a trans-positive membrane potential, the receptor, a negatively charged protein, appears to change its disposition with respect to the membrane. In the second study we consider melittin, an amphipathic peptide containing a generally hydrophobic stretch of 19 amino acids followed by a cluster of four positively charged residues at the carboxy terminus. The hydrophobic region contains two positively charged residues. In response to trans-negative electrical potential, melittin appears to assume a transbilayer position. These findings indicate that electrostatic forces can influence the disposition, and perhaps the orientation, of membrane proteins. Given the inside-negative potential of most or all cells, we would expect transmembrane proteins to have clusters of positively charged residues adjacent to the cytoplasmic ends of their hydrophobic transmembrane segments, and clusters of negatively charged residues just to the extracytoplasmic side. This expectation has been borne out by examination of the few transmembrane proteins for which there is sufficient information on both sequence and orientation. Surface and dipole potentials may similarly affect the orientation of membrane proteins. 相似文献
1000.