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151.
The exposure of apolipoproteins at the surface of human plasma high density lipoproteins (HDL) was assessed by their accessibility to agarose-immobilized forms of trypsin and chymotrypsin. Proteolysis of lipid-free apolipoproteins and the lipoprotein subfractions HDL2 (d = 1.08--1.125 g/ml) and HDL3 (d = 1.125--1.195 g/ml) that differ in lipid-to-protein ratio was compared by polyacrylamide gel electrophoresis and isoelectric focusing of the apolipoproteins and peptide fragments and by quantitation of the various carboxyl-terminal groups formed. Gel filtration of the proteolyzed lipoproteins on Sephadex G-150 column indicated that more than 90% of the apolipoproteins and peptides remain associated with lipoprotein complexes. Proteolysis of lipoproteins occurred more slowly and with less fragmentation of the lipoproteins and apolipoproteins than proteolysis of thelipid-free apolipoproteins or the proteolysis of lipoproteins by soluble proteases reported by other investigators. The difference in lipid content of HDL2 and HDL3 made little difference in their proteolysis. Proteolysis of the lipoproteins by agarose-trypsin was more rapid at 37 degrees C than at 22 degrees C, but the proteolytic products were similar and differed from the products from the lipid free proteins. Peptide fragments from lipoproteins were larger than those from lipid-free proteins, which suggests masking of potentially cleavable groups by lipid. The amounts (mol/g protein) of new carboxyl-terminal tyrosine and phenylalanine released by agarose -chymotrypsin were much greater from the lipid-free proteins, but about 3/4 of the tryptophan residues were inacessible in both lipoproteins and lipid-free proteins. In agarose-trypsin digestion, lysine residues were slightly more masked than arginine in the absence of lipids and much more so in the lipoproteins. However, in the lipoproteins apoA-II, which contains lysine but no arginine, was cleaved more rapidly and extensively by agarose-trypsin than apoA-I. 相似文献
152.
Fluorescence polarization studies of porcine mitochondrial malate dehydrogenase labeled with fluorescein isothiocyanate or fluorescamine indicated a concentration-dependent dissociation of the dimeric molecule with a KD OF 2 X 10(7) N at pH 8.0. These results were confirmed by the concentration dependence of the stability of the enzyme at elevated temperatures and the creation of hybrid molecules with fluorescein and Rhodamine B labeled subunits, in which energy transfer was observed. The binding of NADH resulted in a small shift of the subunit dissociation curve toward monomer, demonstrating that monomer has twice the affinity for reduced coenzyme. NAD+ binding prevented dissociation of the dimer, even at concentrations below 10(-8) N. These results indicate that binding of reduced or oxidized coenzymes results in different conformation changes, which are transferred to the subunit interface. 相似文献
153.
Intracellular transport of the transmembrane glycoprotein G of vesicular stomatitis virus through the Golgi apparatus as visualized by electron microscope radioautography 总被引:4,自引:3,他引:1 下载免费PDF全文
J J Bergeron G J Kotwal G Levine P Bilan R Rachubinski M Hamilton G C Shore H P Ghosh 《The Journal of cell biology》1982,94(1):36-41
The intracellular migration of G protein in vesicular stomatitis virus-infected cells was visualized by light and electron microscope radioautography after a 2-min pulse with [3H]mannose followed by nonradioactive chase for various intervals. The radioactivity initially (at 5-10 min) appeared predominantly in the endoplasmic reticulum, and the [3H]mannose-labeled G protein produced was sensitive to endoglycosidase H. Silver grains were subsequently (at 30-40 min) observed over the Golgi apparatus, and the [3H]mannose-labeled G protein became resistant to endoglycosidase H digestion. Our data directly demonstrate the intracellular transport of a plasmalemma-destined transmembrane glycoprotein through the Golgi apparatus. 相似文献
154.
155.
The biochemical profile of rat testicular tissue as measured by magic angle spinning 1H NMR spectroscopy 总被引:1,自引:0,他引:1
The testis is the principal organ of male fertility, responsible for the production of spermatozoa and their maturation into sperm. However, the underlying biochemistry of the testis is relatively understudied. The fluidic and homogeneous nature of the testis makes it an ideal organ for high resolution magic angle spinning (MAS) 1H NMR spectroscopy. In this study we have catalogued the low molecular weight metabolites. The testis contains large amounts of creatine, of which a substantial proportion was shown to be extracellular using bipolar gradients to measure apparent diffusion coefficients. The tissue also contained relatively high amounts of uridine. 相似文献
156.
157.
The endoplasmic reticulum (ER) can elicit proapoptotic signalling that results in transmission of Ca(2+) to the mitochondria, which in turn stimulates recruitment of the fission enzyme DRP1 to the surface of the organelle. Here, we show that BH3-only BIK activates this pathway at the ER in intact cells, resulting in mitochondrial fragmentation but little release of cytochrome c to the cytosol. The BIK-induced transformations in mitochondria are dynamic in nature and involve DRP1-dependent remodelling and opening of cristae, where the major stores of cytochrome c reside. This novel function for DRP1 is distinct from its recognized role in regulating mitochondrial fission. Selective permeabilization of the outer membrane with digitonin confirmed that BIK stimulation results in mobilization of intramitochondrial cytochrome c. Of note, BIK can cooperate with a weak BH3-only protein that targets mitochondria, such as NOXA, to activate BAX by a mechanism that is independent of DRP1 enzyme activity. When expressed together, BIK and NOXA cause rapid release of mobilized cytochrome c and activation of caspases. 相似文献
158.
159.
A central feature of the serpin inhibition mechanism is insertion of the reactive center loop into the central beta-sheet (beta-sheet A). This insertion also occurs when the reactive center loop is cleaved without protease inhibition. Using this effect, we have measured the enthalpy (DeltaH) of loop cleavage and insertion for plasminogen activator inhibitor 1 (PAI-1) as -38 kcal/mol. Because loop insertion can be blocked by incorporating a peptide into the central beta-sheet, it was possible to assign -7 kcal/mol to loop cleavage and -31 kcal/mol to loop insertion. These values are lower than values reported for the serpins alpha 1 -proteinase inhibitor and antithrombin of -53 to -63 kcal/mol, respectively, for loop insertion with negligible enthalpy for loop cleavage. A free energy difference of -9 kcal/mol has been reported between the active and spontaneously loop inserted "latent forms" of PAI-1, which is significantly smaller in magnitude than the -31 kcal/mol of enthalpy we measured for loop insertion. Because the enthalpy should relate closely to those regions of PAI-1 that have moved to lower potential energy, a difference distance matrix is presented that identifies regions of PAI-1 that move during loop insertion. 相似文献
160.
Johnston RA Mizgerd JP Shore SA 《American journal of physiology. Lung cellular and molecular physiology》2005,288(1):L61-L67
Ozone (O(3)), a common air pollutant, induces airway inflammation and airway hyperresponsiveness. In mice, the neutrophil chemokines KC and macrophage inflammatory protein-2 (MIP-2) are expressed in the lungs following O(3) exposure. The purpose of this study was to determine whether CXCR2, the receptor for these chemokines, is essential to O(3)-induced neutrophil recruitment, injury to lungs, and increases in respiratory system responsiveness to methacholine (MCh). O(3) exposure (1 ppm for 3 h) increased the number of neutrophils in the bronchoalveolar lavage fluid (BALF) of wild-type (BALB/c) and CXCR2-deficient mice. However, CXCR2-deficient mice had significantly fewer emigrated neutrophils than did wild-type mice. The numbers of neutrophils in the blood and concentrations of BALF KC and MIP-2 did not differ between genotypes. Together, these data suggest CXCR2 is essential for maximal chemokine-directed migration of neutrophils to the air spaces. In wild-type mice, O(3) exposure increased BALF epithelial cell numbers and total protein levels, two indirect measures of lung injury. In contrast, in CXCR2-deficient mice, the number of BALF epithelial cells was not increased by O(3) exposure. Responses to inhaled MCh were measured by whole body plethysmography using enhanced pause as the outcome indicator. O(3) exposure increased responses to inhaled MCh in both wild-type and CXCR2-deficient mice 3 h after O(3) exposure. However, at 24 h after exposure, responses to inhaled MCh were elevated in wild-type but not CXCR2-deficient mice. These results indicate CXCR2 is essential for maximal neutrophil recruitment, epithelial cell sloughing, and persistent increases in MCh responsiveness after an acute O(3) exposure. 相似文献