Association of the intestinal brush-border membrane phospholipase A2 and lysophospholipase activities (phospholipase B) with a stalked membrane protein

We have attempted to determine the size and membrane orientation of a recently described rat jejunal brushborder protein possessing phospholipase A₂ and lysophospholipase activities (phospholipase B) (Pind, S. and Kuksis, A. [1988]Biochim. Biophys Acta 938, 211–221). The phospholipase A₂ and lysophospholipase activities were renatured following nonreducing sodium dodecyl sulphate polyacrylamide gel electrophoresis of the total membrane proteins and were shown to migrate as a component of a protein band having a relative molecular mass of 170 kDa. This band accounted for approximately 1% of the total Coomassie Blue staining proteins. Phospholipase B was also shown to be solubilized from the membranes, in an active form, by a proteolytic digestion with papain. Papain solubilization resulted in a loss of the hydrophobic properties observed for the intact phospholipase. These results suggest that the active site of the phospholipase projects from the luminal surface of the membrane vesicles. In support of this, phospholipase activity towards exogenous, detergent-solubilized phosphatidylcholine was demonstrated under conditions in which the membranes remained intact. We conclude that the phospholipase B has the characteristics of a stalked, brush-border membrane protein and may be considered as another digestive enzyme anchored in this membrane.     

Molecular species of glycerophospholipids and sphingomyelins of human erythrocytes: Improved method of analysis

This study reports the application of modern methods of molecular species analysis in determination of the structure of both major and minor glycerophospholipids and sphingomyelins of human erythrocytes. Individual phospholipid classes were resolved from total lipid extracts by thin-layer chromatography. Diradylglycerols were released by phospholipase C and converted into trimethylsilyl ethers, which were resolved into the alkenylacyl, alkylacyl and diacylglycerol subclasses by normal phase high performance liquid chromatography. Molecular species of diradylglycerols and ceramides were quantitated according to carbon and double bond number by gas liquid chromatography using a fused silica capillary column wall-coated with bonded RTx-2330. The molecular species of ceramides were determined by GC/MS. The diradyl glycerophosphocholines contained 93.0% diacyl, 4.6% alkylacyl and 2.5% alkenylacyl, white the diradyl glycerophosphoethanolamines were made up of 48.8% diacyl, 47.8% alkenylacyl and 3.4% alkylacyl subclasses. Analysis of the molecular species showed that the long chain polyunsaturated acids were mainly combined with C₁₆ in all diradyl GPC subclasses and in diacyl GPE, while in the alkylacyl and alkenylacyl GPE and in diacyl glycerophosphoinositol and diacyl glycerophosphoserine they were combined mainly with C₁₈ saturated fatty chains. In addition to the C₁₆ and C₁₈ alkyl and alkenyl, the ether fractions also contained significant proportions of C₂₀, C₂₂ and C₂₄ chains. The molecular species of the ceramide moieties of the SPH were made up largely of mono- and diunsaturated species. Over 200 molecular species were identified and quantitated in a representative sample of human red blood cells.     

Molecular species of glycerophospholipids and sphingomyelins of human plasma: Comparison to red blood cells

In addition to diacyl glycerophosphocholine and sphingomyelin, human plasma also contains small amounts of other glycerophospholipids, which may have special metabolic function. The structure and origin of these minor plasma lipids has not been determined. Knowledge of the detailed composition of the phospholipids of red blood cells (Myheret al., Lipids 24, 1989) permits evaluation of one of the possible sources. This study reports the detailed analyses of plasma glycerophospholipids made in parallel to those of the erythrocyte lipids obtained from the same blood using HPLC and GLC methods. The proportions of the major phospholipid classes in the plasma and erythrocytes were similar to published values, including the essential absence of diradyl glycerophosphoserine from plasma. Plasma diradyl glycerophosphocholine contained 93.0% diacyl, 3.4% alkylkacyl and 3.6% alkenylacyl, whereas the diradyl glycerophosphoethanolamine consisted of 71.8% alkenylacyl, 19.9% diacyl and 8.3% alkylacyl subclasses. The diradyl glycerophosphoinositol was 100% diacyl. The content of the minor subclasses of plasma diradyl glycerophosphocholine is similar to that of the red cells, but the ether content of the diradyl glycerophosphoethanolamine is higher in plasma than in cells. The lipid ether subclasses of plasma glycerophospholipids also contained a higher proportion of the C₂₀, C₂₂ and C₂₄ alkyl and alkenyl chains than those of the cells. Furthermore, the C₁₆ and C₁₈-containing species in diradyl glycerophosphoethanolamine subclasses varied with the nature of the polyunsaturated acid, whereas in diradyl glycerophosphocholine subclasses the polyunsaturated acids were combined with the C₁₆ and C₁₈ acids in equal proportions. The significant differences in the molecular species of glycerophospholipids and sphingomyelin between plasma and red cells would appear to limit any direct transfer or equilibration of their lipid components.     

On the Lambropoulos-Luco's δ-“no go” conjecture in variational flux synthesis

The Lambropoulos-Luco's δ-“no go” conjecture and related controversies in the domain of the variational flux synthesis with discontinuous trial functions are completely resolved in terms of the functionals, ^(±)δ⁽ⁿ⁾(x − x_o), in the frame of the new spaces of functionals, which are topological dual spaces of discontinuous complex valued functions spaces occurring with left and right continuities.     

Spectral factors in the perception of vowel quantity in Icelandic

The aim of this study was to clarify the effect of heating rate on the development of both transient and residual stresses in investment molds. Solid, cylindrical, gypsum-based molds were modeled and theoretical calculations made of temperature distributions with a constant heating rate. These calculations used experimental thermal diffusivity data obtained with a laser flash method. The simulations calculated transient thermal stresses during heating and at the end of heating for two surface conditions: an unrestricted surface, and a surface restricted by a casting ring. The simulation model developed nonuniform strains and stresses at casting temperature; tangential stress was compressive at the surface and tensile at the mid-point for the unrestricted surface model. The surface restricted model developed compressive tangential stresses throughout the mold at the casting temperature. This resulted in significant thermal strain differences compared to the magnitudes of expansion of the mold due to heating.     

Gudmundur Finnbogason, "Sympathetic understanding," and early Icelandic psychology.

Gudmundur Finnbogason (1873-1944) was a pioneer of Icelandic psychology. He was educated at the University of Copenhagen where he finished his M.A. in 1901 in philosophy, specializing in psychology. During the years 1901-1905, Finnbogason played a major role in establishing and shaping the future of primary education in Iceland. He defended his doctoral thesis on "sympathetic understanding" at the University of Copenhagen in 1911. This work deals with the psychology of imitation. In it Finnbogason defends the view that imitation is basically perception so that there is a direct link from perception to motor behavior. Through imitation people tend to assume the countenance and demeanor of other people, thus showing, in Finnbogason's terminology, "sympathetic understanding." Finnbogason's theory of imitation in many respects anticipates contemporary approaches to the psychology of imitation. In 1918 Finnbogason became professor of applied psychology at the recently founded University of Iceland. Here he attempted to establish psychology as an independent discipline. In this he was unsuccessful; his chair was abolished in 1924. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Auditory and linguistic factors in the perception of voice offset time as a cue for preaspiration

Previous research [J. Pind, Acta Psychol. 89, 53-81 (1995)] has shown that preaspiration in Icelandic, an [h]-like sound inserted between a vowel and the following closure, can be cued by Voice Offset Time (VOffT), a speech cue which is the mirror image of Voice Onset Time (VOT). Research has also revealed that VOffT is much more sensitive to the duration of the neighboring vowel than is VOT [J. Pind, Q. J. Exp. Psychol. 49A, 745-764 (1996)]. This paper explores the hypothesis that it is primarily the perceived quantity of the vowel that is responsible for the effect of the vowel on the perception of preaspiration. This hypothesis is based on the linguistic fact that preaspiration can only follow a phonemically short vowel. This linguistic hypothesis is contrasted with an auditory hypothesis in terms of forward masking. Perceptual experiments show that the perceptual boundaries for preaspiration can be affected either by changing the preceding vowel's duration or its spectrum. If the spectrum of the vowel changes towards that of a long vowel, longer VOffT's are needed for listeners to perceive preaspiration, thus lending support to the linguistic hypothesis.     

Molecular species of glycerolipids of ehrlich ascites cells and of their fat granules

Ehrlich ascites cells were grown in mice and were isolated by centrifugation of the ascites fluid. The cells were lysed with distilled water, and the floating fat particles were collected by centrifugation. The particles contained about 90% neutral and 10% polar lipid. The neutral lipid was made up of about 50% triacylglycerol, 30% alkyldiacylglycerol, 3% cholesteryl esters, 3% free cholesterol and 4% free diacylglycerols. The phospholipid fraction was comprised of about 50% phosphatidylcholine, 35% phosphatidylethanolamine, 10% sphingomyelin and small amounts (less than 5% total) of serine and/or inositol phosphatides. The triacylglycerol and alkyldiacylglycerol fractions possessed total carbon number and fatty acid compositions closely similar to these reported in the literature for whole ascites cells and for a cell membrane preparation. Likewise, the fatty acid composition of phospholipids from the granules in general was similar to that reported for Ehrlich ascites cells. On the basis of the polar and neutral lipid ratio, the lipid granules of the ascites cells were calculated to possess lipid core diameters of 30–50 nm, which were 40–70 times smaller than those (up to 2μ) measured for the lipid granules of the intact cells by electron microscopy. The characterization of the lipid composition of the Ehrlich ascites lipid granules was completed by determing the molecular species composition of the diacyl, alkylacyl and alkenylacyl phosphatidylethanolamines and of the diacyl and alkylacyl phosphatidylcholines of the ascites cells. It is concluded that the alkyldiacylglycerols of the Ehrlich ascites cells occur largely in the cytoplasmic lipid granules, which appear to consist of many particles of the size and structure of very low density lipoproteins enclosed in membranous sacs.