Structural studies of phosvitin in solution and in the solid state

Phosvitin, a highly phosphorylated glycoprotein, represents the major fraction of hen egg yolk phosphoproteins. Circular dichroism, Fourier transform infrared spectroscopy, and Fourier transform infrared photoacoustic and fluorescence spectroscopic methods were employed to determine the secondary structure of the protein in both the solid and solution phases. This was supplemented by a Chou-Fasman type of predictive algorithm for the first 25 residues at the N terminus of the dephosphorylated protein. A three-compartment model consisting of alpha-helical, beta-sheet, and beta-turn components with beta-turns occurring at the interface between alpha-helical and beta-sheet regions in the proximity of O-phosphoserine residues is suggested from the combined analyses. Beta-sheets appear to be the dominant secondary structural component in phosvitin in the solid and solution phases. The suggested model bears many similarities to other phosphoproteins reported in the literature. The secondary structure of phosvitin is observed to be sensitive to environmental factors as previously reported although the present studies differ in some respects from earlier results. Preliminary results suggest that Ca2+ ions trigger a decrease in beta-sheet structure at pH 2.     

Amylase activity, glycoprotein and electrolyte concentration in rat's submaxillary salivary gland during heat acclimation.

1. Amylase activity, glycoproteins, Na and K concentrations were measured in submaxillary salivary gland of the rat during heat acclimation (34 degrees C). 2. Acclimation resulted in a decrease in glycoprotein concentration and amylase activity, whereas Na and K concentrations and the Na/K ratio increased. 3. It is suggested that heat acclimation results in an increase in glandular activity leading to increased water secretion and depletion of the glycoprotein store. The decrease in amylase activity is probably due to liver atrophy which occurs during prolonged heat exposure.     

A simple, inexpensive, and precise microcell for the exchange dialysis and equilibrium dialysis of small samples

A simple equilibrium dialysis cell may be quickly prepared from common, inexpensive microcentrifuge tubes. The resulting cell is easy to use and precise enough for quantitative dialysis studies of small samples (<50 μl). In addition, by using a portion of the cell, exchange dialysis of small samples can easily be done.     

Effects of diets enriched in linoleic acid and its peroxidation products on brain fatty acids,oxylipins, and aldehydes in mice

Background

Linoleic acid (LA) is abundant in modern industrialized diets. Oxidized LA metabolites (OXLAMs) and reactive aldehydes, such as 4-hydroxy-2-nonenal (4-HNE), are present in heated vegetable oils and can be endogenously synthesized following consumption of dietary LA. OXLAMs have been implicated in cerebellar degeneration in chicks; 4-HNE is linked to neurodegenerative conditions in mammals. It unknown whether increasing dietary LA or OXLAMs alters the levels of oxidized fatty acids (oxylipins), precursor fatty acids, or 4-HNE in mammalian brain.

Localization of the major ethidium bromide binding site on tRNA.

Binding of ethidium bromide to Escherichia coli tRNAVal and an RNA minihelix based on the acceptor stem and T-arm of tRNAVal was investigated by 19F and 1H NMR spectroscopy of RNAs labeled with fluorine by incorporation of 5-fluorouracil. Ethidium bromide selectively intercalates into the acceptor stem of the tRNAVal. More than one ethidium bromide binding site is found in the acceptor stem, the strongest between base pairs A6:U67 and U7:A66. 19F and 1H spectra of the 5-fluorouracil-substituted minihelix RNA indicate that the molecule exists in solution as a 12 base-paired stem and a single-stranded loop. Ethidium bromide no longer intercalates between base pairs corresponding to the tRNAVal acceptor stem in this molecule. Instead, it intercalates between base pairs at the bottom of the long stem-loop structure. These observations suggest that ethidium bromide has a preferred intercalation site close to the base of an RNA helical stem.     

Automated Electron Microscope Tomography of Frozen–Hydrated Chromatin: The Irregular Three-Dimensional Zigzag Architecture Persists in Compact, Isolated Fibers

The potential of electron microscope tomography as a tool for obtaining three-dimensional (3D) information about large macromolecular assemblies is greatly extended by automation of data collection. With the implementation of automated control of tilting, focusing, and digital image recording described here, tilt series of frozen–hydrated specimens can be collected with the requisite low dose. Long chromatin fibers were prepared in 90 mM monovalent ions to maintain a fully compact conformation, and after vitrification were completely contained within the ice layer. Tilt series of this material were recorded at 5° tilt increments between +60° and −60°, with a cumulative dose of ≈35 e⁻/Ųfor the series. This extremely low dose data was successfully aligned, then reconstructed by weighted backprojection. The underlying architecture of the fibers is an irregular 3D zigzag of interconnected nucleosomes, with the linker DNA between successive nucleosomes in a largely extended conformation. The visualization of this structural motif within long, frozen–hydrated chromatin fibers at relatively high salt extends our previous studies on small fragments at low ionic strength and is in agreement with the observation of this architecture in chromatin fibersin situin sectioned nuclei.     

HTLV-Ⅰ tax反义RNA逆转小鼠神经纤维瘤

来源于转基因小鼠 (HTLV ⅠLTRtax基因 )的神经纤维瘤细胞系的细胞中 ,外源基因HTLV I tax高表达产生mRNA和蛋白质 ,使细胞出现转化表型 .当将反向插入了HTLV I taxcDNA的逆转录病毒导入这种细胞后 ,转录生成的反义RNA可抑制tax基因的表达 ,mRNA和蛋白质均减少 40 %强 ;细胞的形态和生长特征也随之发生明显变化 ;原先由Tax蛋白质激活的基因如GM -CSF ,IL -6,LT/TNF (蛋白质水平 ) ,c -myc和LIF(mRNA水平 )等的表达均下调 ;M -CSF(蛋白质水平 )和原癌基因c src(mRNA水平 )的表达上升 ;β 肌纤蛋白mRNA则不受影响 .这些变化可能是由于tax反义RNA降低了细胞内Tax蛋白质浓度的缘故 .这表明HTLV ⅠTax蛋白质维持转化细胞的形态、生长和增殖起关键性作用 ;由Tax蛋白质激活的细胞内源基因的表达受阻 ,则是转基因小鼠发生神经纤维瘤的原因 .