Lipid/myelin basic protein multilayers. A model for the cytoplasmic space in central nervous system myelin

A multilayered complex forms when a solution of myelin basic protein is added to single-bilayer vesicles formed by sonicating myelin lipids. Vesicles and multilayers have been studied by electron microscopy, biochemical analysis, and X-ray diffraction. Freeze-fracture electron microscopy shows well-separated vesicles before myelin basic protein is added, but afterward there are aggregated, possibly multilayered, vesicles and extensive planar multilayers. The vesicles aggregate and fuse within seconds after the protein is added, and the multilayers form within minutes. No intra-bilayer particles are seen, with or without the protein. Some myelin basic protein, but no lipid, remains in the supernatant after the protein is added and the complex sedimented for X-ray diffraction. A rather variable proportion of the protein is bound. X-ray diffraction patterns show that the vesicles are stable in the absence of myelin basic protein, even under high g-forces. After the protein is added, however, lipid/myelin basic protein multilayers predominate over single-bilayer vesicles. The protein is in every space between lipid bilayers. Thus the vesicles are torn open by strong interaction with myelin basic protein. The inter-bilayer spaces in the multilayers are comparable to the cytoplasmic spaces in central nervous system myelins . The diffraction indicates the same lipid bilayer thickness in vesicles and multilayers, to within 1 A. By comparing electron-density profiles of vesicles and multilayers, most of the myelin basic protein is located in the inter-bilayer space while up to one-third may be inserted between lipid headgroups. When cytochrome c is added in place of myelin basic protein, multilayers also form. In this case the protein is located entirely outside the unchanged bilayer. Comparison of the various profiles emphasizes the close and extensive apposition of myelin basic protein to the lipid bilayer. Numerous bonds may form between myelin basic protein and lipids. Cholesterol may enhance binding by opening gaps between diacyl-lipid headgroups.     

The Electrical Conductivity of Bovine Milk in Mastitis Diagnosis

The electrical conductivity (EC) of milk is mainly a function of the electrolyte concentration in the milk and therefore raised in mastitis. The present investigation was aimed at elaborating, if possible, a diagnostic model for screening purposes based on EC determinations and consistent with the diagnostic procedures and interpretations commonly used in laboratory milk diagnosis in the Nordic countries (Klastrup 1975). According to this diagnosis (here called reference diagnosis) cell numbers above 300,000/ml (cell count or the corresponding CMT-score) in foremilk quarter samples during the main part of the lactation period and significantly above the lowest value on within-udder comparison during late lactation are considered indicative of mastitis and bacteriological examinations are made when called for.     

Expression of L3T4 molecules on Lyt-2+, class II-restricted antigen-specific T suppressor lymphocytes

Three bovine serum albumin-specific Lyt-2⁺ T suppressor (Ts) cell clones from CBA/J mice have been analyzed with regard to expression of L3T4 molecules. All three Ts-cell clones can be stained with monoclonal antibodies (mAb) to L3T4. Tested for the two clones restricted to recognition of E^k determinants, antigen-specific proliferation on antigen-presenting cells, but not the proliferation induced by conditioned medium can be inhibited by L314-specific mAb. In a similar way, Ts-cell cytolytic effector functions can be blocked by L3T4-specific mAb. Thus L3T4 structures seem to play a role in Ts-cell functions. Furthermore, the data support the view that L3T4 expression can be a property of class II-restricted T cells irrespective of their Lyt phenotype.     

Electron microscopic cytochemical localization ofα-hydroxyacid oxidase in rat liver

Summary The substrate specificity and the intraperoxisomal localization of -hydroxyacid oxidase in rat liver has been investigated cytochemically by the cerium technique and biochemically with a luminometric assay. Rat liver is fixed by perfusion with a low concentration (0.25%) of glutaraldehyde and vibratome sections are incubated for 60 min at 37°C in a medium containing 3 mM CeCl₃, 100 mM NaN₃ and 5 mM of an -hydroxyacid in 0.1M of one of the following buffers: Pipes, Mops, Na-cacodylate,Tris-maleate, all adjusted to pH 7.8. Ten different -hydroxyacids with a chain length between 2 and 8 carbon atoms were tested. The best results were obtained with glycolic, argininic andl--isocaproic acids. These cytochemical findings were confirmed also biochemically using purified peroxisomal fractions isolated by gradient centrifugation in metrizamide. The pattern of the intraperoxisomal localization of the enzyme was influenced markedly by the type of buffer used for the cytochemical incubation. Whereas in theTris-maleate medium both the cores and the matrix stained with the same intensity, with all other buffers the reaction in cores was more prominent. The staining of cores was abolished by pretreating sections inTris-maleate (pH 7.8) or alkaline pyrophosphate buffers. These observations establish the substrate specificity of -hydroxyacid oxidase in rat liver and demonstrate the delicate association of this enzyme with the crystalline cores and the matrix of peroxisomes in rat liver.Abbreviations -HAOX l-hydroxyacid oxidase - Argininic acid l--hydroxy--guanidinovaleric acid - Pipes piperazine-N,N-bis(2ethane sulfonic acid) - Mops 3(N-morpholino) propane sulfonic acid - Tris tris-(hydroxymethyl)-aminomethane - Luminol 5-amino-2,3 dihydrophthalazine-1,4-dione - GA glutaraldehyde     

Autoaggregating Yersinia enterocolitica express surface fimbriae with high surface hydrophobicity

For 13 strains of Yersinia enterocolitica, there was a good correlation between the production of the broad-spectrum, mannose-resistant Yersinia haemagglutinin (MR/Y HA), the presence of fimbriae and high surface hydrophobicity. Each of these characters was expressed in cultures grown at low (less than 32 degrees C) but not at high (Greater than 35 degrees C) temperatures.     

The incorporation of selenium and alterations of macro- and trace element levels in individual blood cells following supplementation with sodium selenite and vitamin E

Significant alterations in the selenium content of erythrocytes, thrombocytes, and neutrophil granulocytes were observed following a daily supplementation of 200 μg Se + 100 mg vitamin E during a period of 2 months. The neutrophil granulocytes incorporated more selenium than the thrombocytes. The iron content of the thrombocytes decreased on selenium supplementation, while the opposite was noted for the neutrophil granulocytes. The glutathione peroxidase activity was not significantly changed during the period of observation.     

Improved demonstration of exocytotic profiles in glomus cells of rat carotid body after perfusion with glutaraldehyde fixative containing a high concentration of potassium

Extensive secretion by exocytosis was demonstrated in the glomus (type I) cells of the adult rat after perfusion of carotid bodies with a potassium-rich (high K) glutaraldehyde fixative. Similar secretory profiles were very rare with a glutaraldehyde fixative containing a low concentration of potassium (low K). The increase in the incidence of exocytotic profiles in glomus cells with the high K fixative was highly significant, whereas no statistical difference could be observed in the incidence of coated pits with the different fixatives. Exocytotic profiles were characterized by the following features: (1) they predominated in non-synaptic regions, but were occasionally observed near synapses between two glomus cells; they were not observed near synapses between glomus cells and nerve terminals; (2) extruded electron-dense material associated with coating of the cell membrane was frequent; (3) different stages of dissolution of the extruded granule material was evident. The possible role of exocytosis as a mode of secretion in the glomus cells and the characteristics of the new high K-glutaraldehyde fixative are discussed.     

Les effets de recristallisation sur la paroi des Involutinidae (Foraminifères) triasiques

The different types of recrystallization which can be observed in the Triassic involutinids should be considered in the taxonomic treatment of this foraminiferal family. If the diagenetic modifications of the test are neglected the same form could be placed into different suborders. Our inclusion of the genusTriasina Majzon in the Involutinidae proposed earlier on purely morphologic grounds, seems to be supported by the fact that the same types of recrystallization exist inTrocholina, Involutina undTriasina.