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Results of transgenetic studies argue that the scrapie isoform of the prion protein (PrPSc) interacts with the substrate cellular PrP (PrPC) during conversion into nascent PrPSc. While PrPSc appears to accumulate primarily in lysosomes, caveolae-like domains (CLDs) have been suggested to be the site where PrPC is converted into PrPSc. We report herein that CLDs isolated from scrapie-infected neuroblastoma (ScN2a) cells contain PrPC and PrPSc. After lysis of ScN2a cells in ice-cold Triton X-100, both PrP isoforms and an N-terminally truncated form of PrPC (PrPC-II) were found concentrated in detergent-insoluble complexes resembling CLDs that were isolated by flotation in sucrose gradients. Similar results were obtained when CLDs were purified from plasma membranes by sonication and gradient centrifugation; with this procedure no detergents are used, which minimizes artifacts that might arise from redistribution of proteins among subcellular fractions. The caveolar markers ganglioside GM1 and H-ras were found concentrated in the CLD fractions. When plasma membrane proteins were labeled with the impermeant reagent sulfo-N-hydroxysuccinimide-biotin, both PrPC and PrPSc were found biotinylated in CLD fractions. Similar results on the colocalization of PrPC and PrPSc were obtained when CLDs were isolated from Syrian hamster brains. Our findings demonstrate that both PrPC and PrPSc are present in CLDs and, thus, support the hypothesis that the PrPSc formation occurs within this subcellular compartment

The compositions and concentrations of lipid classes, fatty acids and tocopherols were determined in the lipids from Spirulina platensis. Total lipids (TL) recovered using chloroform : methanol (2:1, v/v) were found to be 163.5 g/kg (on dry weight basis). The level of neutral lipids was the highest, followed by glycolipids and phospholipids, respectively. Among TL and lipid classes, palmitic, gamma-linolenic and linoleic acids were the dominating fatty acids. Compared with the neutral lipids, the polar fractions were generally characterised by higher percentages of saturated fatty acids. The recovered lipids were characterised by high percentage of tocopherols, wherein alpha-tocopherol constituted about 73% of total tocopherols present, the rest having been gamma-tocopherol. Spirulina platensis lipids exhibited a strong radical scavenging activity towards stable DPPH free radicals, whereas 27% of DPPH radicals were quenched after 2 h incubation. TL and lipid classes inhibited the growth of different microorganisms except gram-negative bacteria. At high concentrations, the tested lipids appeared more effective against A. niger (28.3+/-1.53 mm).

Arabinogalactan-proteins (AGPs) are a class of proteoglycans found in cell secretions and plasma membranes of plants. Attention is currently focused on their structure and their potential role in growth and development. We present evidence that two members of a major class of AGPs, the classical AGPs, AGPNa1 from styles of Nicotiana alata and AGPPc1 from cell suspension cultures of Pyrus communis, undergo C-terminal processing involving glycosylphosphatidylinositol membrane anchors. The evidence is that (i) the transmembrane helix at the C terminus predicted from the cDNA encoding these proteins is not present--the C-terminal amino acid is Asn87 and Ser97 for AGPNa1 and AGPPc1, respectively: (ii) both AGP protein backbones are substituted with ethanolamine at the C-terminal amino acid: and (iii) inositol, glucosamine, and mannose are present in the native AGPs. An examination of the deduced amino acid sequences of other classical AGP protein backbones shows that glycosylphosphatidylinositol-anchors may be a common feature of this class of AGPs

We report on the characteristics of seed oils, nutrients and mineral contents of seeds from three varieties of karela, Momordica charantia. Most of the physicochemical characteristics were significantly affected by the variety. Seed oils of all varieties displayed a high degree of unsaturation as unsaturated fatty acids represented more than 72%, alpha-eleostearic acid having been detected in the amount of 50.36-53.22%. Other fatty acids identified in the seeds were palmitic, stearic, oleic and linoleic acids. Acylglycerol classes were estimated to be monoacylglycerols (1.18-2.01%), diacylglycerols (1.83-2.98%), and triacylglycerols (91.11-93.03%), whereas lipid classes included neutral lipids (86.83-91.09%), glycolipids (4.37-7.43%), and phospholipids (3.22-4.62%). All varieties contained large amounts of lipids (33.93-36.21%) and proteins (18.23-21.36%) as well as potentially useful amounts of calcium (383.45-440.96 microg/g), iron (41.10-45.03 microg/g), and other essential minerals.

The het-c locus contains different alleles that elicit nonallelic vegetative incompatibility through specific interactions with alleles of the unlinked loci het-e and het-d. The het-c2 allele has been cloned. It encodes a 208-amino acid polypeptide that is similar to a glycolipid transfer protein purified from pig brain. Disruption of this gene drastically impairs ascospore production in homozygous crosses, and some mutants exhibit abnormal branching of apical hyphae. The protein encoded by het-c2 is essential in the biology of the fungus and may be involved in cell-wall biosynthesis.

Syringolides are glycolipid elicitors produced by Gram-negative bacteria expressing Pseudomonas syringae avirulence gene D. The syringolides mediate gene-for-gene complementarity, inducing the hypersensitive response only in soybean plants carrying the Rpg4 disease resistance gene. A site(s) for 125I-syringolide 1 was detected in the soluble protein fraction from soybean leaves, but no evidence for ligand-specific binding to the microsomal fraction was obtained. The Kd value for syringolide 1 binding with the soluble fraction was 8.7 nM, and binding was greatly reduced by prior protease treatment or heating. A native gel assay was also used to demonstrate ligand-specific binding of labeled syringolide 1 with a soluble protein(s). Competition studies with 125I-syringolide 1 and several structural derivatives demonstrated a direct correlation between binding affinity to the soluble fraction and elicitor activity. However, differential competition binding studies disclosed no differences in syringolide binding to soluble fractions from Rpg4/Rpg4 or rpg4/rpg4 soybean leaves. Thus, the observed binding site fulfills several criteria expected of an intracellular receptor for the syringolides, but it is most likely not encoded by the Rpg4 gene. Instead, the Rpg4 gene product may function subsequent to elicitor binding, possibly in intracellular signal transduction

An extract of the chloromonad Heterosigma carterae (Raphidophyceae), cultivated in natural seawater, contained a complex mixture of sulfoquinovosyl diacylglycerols. Palmitoyl (16:0), three isomers of hexadecenoyl (16:1 cis Δ9, Δ11, Δ13), and eicosapentenoyl (20:5) were found to be the main fatty acyl substituents. Exact double‐bond sites were determined by mass spectrometry analysis of the corresponding nicotinyl derivatives. Four major sulfoquinovosyl diacylglycerol components were partially purified and identified as 1–4 by interpretation of their nuclear magnetic resonance and mass spectral data. In addition, complete analysis of the H. carterae sulfoquinovosyl diacylglycerols was performed using high‐performance liquid chromatography combined with electrospray tandem mass spectrometry.

The glycosyl-phosphatidylinositol (GPI) anchor of the Trypanosoma brucei variant surface glycoprotein (VSG) is unique in having exclusively myristate as its fatty acid component. We previously demonstrated that the myristate specificity is the result of two independent pathways. First, the newly synthesized free GPI, which is not myristoylated, undergoes fatty acid remodeling to replace both its fatty acids with myristate. Second, the myristoylated precursor, glycolipid A, undergoes a myristate exchange reaction, detected by the replacement of unlabeled myristate by [3H]myristate. Remodeling and exchange have different enzymatic properties and apparently occur in different subcellular compartments. We now demonstrate that the GPI anchor linked to VSG is the major substrate for myristate exchange. VSG can be efficiently labeled with [3H]myristate by exchange in the presence of cycloheximide, an inhibitor that prevents new VSG synthesis and thus anchor addition to protein. Not only is newly synthesized VSG subject to exchange, but mature VSG, possibly recycling from the cell surface, also undergoes myristate exchange

Electrical measurements were carried out to investigate the contribution of chloroplast lipids to the passive proton permeability of both the thylakoid and inner-envelope membranes. Permeability coefficient and conductance to protons were measured for solvent-free bilayers made from monogalactosyldiglyceride: digalactosyldiglyceride: sulfoquinovosyldiglyceride: phosphatidylglycerol (2:1:0.5:0.5, w/w) in the presence of a pH gradient of 7.4/8.1. The permeability coefficient for protons in glycolipids was 5.5 +/- 1.1 X 10(-4)cm s-1 (n = 14). To determine whether this high H+ permeability could be explained by at the presence of lipid contaminants such as weak acids, we investigated the effects of (a) bovine serum albumin, which can remove some amphiphilic molecules such as free fatty acids, (b) 6-ketocholestanol, which increases the membrane dipole potential, (c) oleic acid, and (d) chlorodecane, which increases the dielectric constant of the lipid (C bilayer. Our results show that free fatty acids are inefficient protonophores, as compared with carbonylcyanide-m-chlorphenylhydrazone, and that the hypothesis of a weak acid mechanism is not valid with H glycolipid bilayers. In the presence of deuterium oxide the H+ conductance was reduced significantly, indicating that proton transport through the glycolipid matrix could occur directly by a hydrogen bond process. The passive transport of H+ through the glycolipid matrix is discussed with regard to the activity of the thylakoid ATP synthase and the inner-envelope H+-ATPase

Lipochitooligosaccharides (LCOs) are plant growth regulators that promote at subfemtomolar concentrations cell division in tobacco protoplasts. In response to LCO treatment, tobacco cells release a second growth factor that fully mediates the growth-promoting activities of the initial extracellular LCO stimulus. This diffusible growth factor was isolated from the protoplasts' culture filtrate and shown to be a peptide. We report that the LCO-induced mitogen released by tobacco cells and a synthetic heptadecapeptide derived from region 2 of the tobacco homolog of the early nodulin gene ENOD40 are antigenically related and qualitatively indistinguishable in their ability to stimulate cell division