Lateral Diffusion in an Archipelago: Effects of Impermeable Patches on Diffusion in a Cell Membrane

Lateral diffusion of molecules in lipid bilayer membranes can be hindered by the presence of impermeable domains of gel-phase lipid or of proteins. Effective-medium theory and percolation theory are used to evaluate the effective lateral diffusion constant as a function of the area fraction of fluid-phase lipid and the permeability of the obstructions to the diffusing species. Applications include the estimation of the minimum fraction of fluid lipid needed for bacterial growth, and the enhancement of diffusion-controlled reactions by the channeling effect of solid patches of lipid.     

Inhibition of human seminal fluid and Leishmania donovani phosphatases by molybdate heteropolyanions

Inhibition of a tartrate-resistant acid phosphatase (ACP) from Leishmania donovani and the tartrate-sensitive ACP from human seminal fluid (prostatic ACP) was examined using a series of 13 molybdate-containing heteropolyanions. The heteropolyanions were divided into four groups based on the number of molybdenum atoms they contain: Group I, Mo4; Group II, Mo6-8; Group III, Mo12; Group IV, Mo18. Two of the four groups, those consisting of compounds that contain either an Mo4 unit or an Mo18 unit with a heteroatom in the central cavity, were potent inhibitors and exhibited the highest degree of selectivity against the leishmanial and seminal fluid ACPs. The inhibition of prostatic ACP by complex E2 could be completely reversed by dialysis. Little inhibition of the acid phosphatase, beta-glucuronidase, or alpha-mannosidase from human spleen was observed with complexes B' and E2. For the seminal fluid phosphatase, the Ki values obtained with arsenate and vanadate depended markedly on pH, suggesting that, unlike most other phosphatases, the conformation of the inhibitor binding site on human seminal fluid ACP is pH-dependent. Results of competition experiments performed with various inhibitor pairs indicated that complex D2 binds to the active site of prostatic ACP while complex M binds at some site on the enzyme that affects the active site. Binding of complex M also modifies the affinity of the enzyme for other inhibitors such as vanadate. The potency of several heteropolyanion complexes and their selective inhibition of pathophysiologically significant acid phosphatases indicate that these compounds may have value as tools for study of the structure and function of this class of enzyme and perhaps in the therapy of human disease.     

Gamma/delta T cell receptor positive T cells in the inflammatory joint: lack of association with response to soluble antigens

In patients with inflammatory synovitis, the proliferative response by lymphocytes from synovial fluid to soluble mycobacterial antigens is enhanced relative to those from peripheral blood. Earlier studies suggested that gamma/delta T cell receptor positive (TCR+) T lymphocytes may significantly contribute to the mycobacterial-specific synovial fluid response. We therefore examined the relationship of the T cell proliferative response to Mycobacterium tuberculosis antigens and the presence of gamma/delta TCR+ T cells employing several monoclonal antibodies. No consistent increase of gamma/delta TCR+ T cells was noted in inflammatory synovial fluids or tissues. Nonetheless, lymphocytes from the majority of the synovial fluids proliferated vigorously in response to water-soluble M. tuberculosis antigens. There was no relationship between the percentage of gamma/delta TCR+ T lymphocytes and the intensity of the proliferative response. In contrast, stimulation with whole mycobacterial organisms was capable of enriching the gamma/delta TCR+ cell population obtained from the peripheral blood of tuberculosis skin test positive normal controls and from some inflammatory synovial fluids. These observations do not support a role for mycobacteria reactive gamma/delta TCR+ synovial T lymphocytes in response to soluble mycobacterial antigens or in the local pathogenesis of inflammatory synovitis.     

Low hydration phase properties of phospholipid mixtures

An experimental investigation of the low hydration phase properties of phospholipid mixtures is described. ²H (D₂O) NMR, X-ray diffraction and differential scanning calorimetry have been used to elucidate the phase properties of mixtures of the mixed chain phospholipids palmitoyloleoylphosphatidylcholine (POPC) and palmitoyloleoylphosphatidylethanolamine (POPE). At 10% hydration pure POPE exhibited a H_II phase above 330 K, a fluid lamellar phase below 315 K, and a minimally hydrated crystalline phase below 300 K. For the 1:1 mixture, the samples exhibited only gel or fluid phases between 270 K and 360 K for hydrations in the range 15% to 30%. Below 15% hydration the mixture exhibited two fluid phases with different repeat spacings, as predicted previously.     

The membrane skeleton of erythrocytes: models of its effect on lateral diffusion

The membrane skeleton, a network of structural proteins attached to the cytoplasmic surface of the plasma membrane, hinders lateral diffusion of integral proteins. 2. In some types of cells, such as epithelial cells and nerve cells, the obstruction of lateral diffusion by the membrane skeleton is one of the mechanisms by which proteins are localized to domains on the cell surface. 3. The effect of the membrane skeleton on lateral diffusion may involve steric hindrance, transient binding or both. Three pictures of the effect are reviewed, the discrete barrier model, the continuous barrier model and the transient binding model. 4. Experiments to distinguish the models are discussed.     

Directional Ca2+ effect on stimulation of mucin secretion from chicken trachea in vitro

Chicken tracheal mucosa in vitro transported and incorporated radioactive precursors into mucins, which were secreted at a steady rate into the tracheal lumen. Secretion of mucins labelled with ³⁵S and ³H after pulse-labelling of the mucosal layer with Na₂³⁵SO₄ and d-[1-³H]glucosamine as precursors was an energy-dependent process, as it was strongly inhibited by the action of respiratory-chain inhibitors, an uncoupler of oxidative phosphorylation, a metabolic blocker and a temperature shift from 41°C to 5°C. On the other hand, both cholinergic and parasympathomimetic agents considerably increased the secretion of dual-radiolabelled mucins when applied on the submucosal side of the trachea. The effect of Ca²⁺ was directional, since only high submucosal (3.6 or 18mm) or low luminal (zero or 0.18mm) Ca²⁺ massively enhanced the secretion of radiolabelled mucin compared with the mucin output measured under physiological Ca²⁺ conditions (1.8mm). Whereas application of ionophore A23187 on either side of the trachea significantly increased mucin output, its presence in the appropriate tracheal compartment and under appropriate Ca²⁺ conditions further accentuated the output of radiolabelled mucins. Addition of acetylcholine under appropriate conditions also had an additive effect on the Ca²⁺-stimulated secretion of mucins. Ca²⁺ stimulation of mucin secretion appears to be dependent on the metabolic integrity of the mucosal cells. Mucins secreted in response to high submucosal and low luminal [Ca²⁺] appear to consist of a number of different types of glycoproteins, as judged from their ion-exchange-chromatographic behaviour.     

Ecological distribution of Legionella pneumophila.

Bacteria were concentrated 500-fold from 20-liter water samples collected from 67 different lakes and rivers in the United States. The data suggest that Legionella pneumophila is part of the natural aquatic environment and that the bacterium is capable of surviving extreme ranges of environmental conditions. The data further demonstrate the effectiveness of the direct fluorescent-antibody technique for detecting L. pneumophila in natural aquatic systems. Smears of the concentrated samples were screened microscopically for serogroups of L. pneumophila by the direct fluorescent-antibody technique. Virtually all of the 793 samples were found to be positive by this method. The 318 samples containing the largest numbers of positive bacteria which were morphologically consistent with L. pneumophila were injected into guinea pigs for attempted isolations. Isolates were obtained from habitats with a wide range of physical, chemical, and biological parameters. Samples collected monthly from a thermally altered lake and injected into guinea pigs demonstrated a seasonality of infection, with the highest frequency of infection occurring during the summer months.     

A pulsed NMR study of lipids,bound water and sodium ions in macroscopically-oriented lecithin/water lyotropic liquid crystal model membrane systems

The temperature and orientation dependence of pulsed NMR ‘free induction decay’ signals have been studied in detail for lipid bilayers macroscopically-oriented between glass slides. Results for the lipid molecules (¹H, ³¹P), bound water (²H₂O) and ions dissolved in the aqueous phase (²³Na) are presented. Bilayers of egg-lecithin, dimyristoyl lecithin and potassium oleate have been investigated. In the liquid crystal phase all the signals, including those from bound water and ions exhibit a |3 cos²? ? 1| dependence on orientation of the bilayer normal to the magnetic field. In the case of DML samples, some orientation dependence of both ¹H and ²H signals persists in the gel phase, indicating that the lipid molecules retain a degree of reorientational freedom about their long axes in this phase. At the gel-liquid crystal transition the ²H quadrupole spittings undergo a discontinuous change. Results are interpreted in terms of a model in which water molecules are bound to individual lipid head groups and reorient with them, while sodium ions are located in the aqueous channel between bilayers.