Composition of soluble cuticular lipids and water permeability of cuticular membranes from Citrus leaves

Water permeability and composition of soluble cuticular lipids of isolated cuticular membranes from leaves of Citrus aurantium L. were investigated for 3 successive years. The average water permeability coefficient determined using 169 cuticular membranes was 1.09·10^–7 cm s^–1 with a standard deviation of 0.78·10^–7 cm s^–1. There were no significant differences in water permeability between years. Cuticular membranes are characterized by a great variability in water permeability both within and between years. Both water permeability of individual membranes and variability between membranes are shown to be determined by soluble cuticular lipids contained within the cuticular membranes. The soluble cuticular lipids of Citrus leaves are composed of fatty acids, primary alcohols, esters, and hydrocarbons. They occur in amounts of 9.84 g cm^–2, which represents approx. 3% of the total mass of isolated cuticular membranes. The specific weight of cuticular membranes (365.4 g cm^–1) and total amount of soluble cuticular lipids did not vary significantly between years. Significant differences were observed for the amounts and composition of the constituent classes of lipids. Six homologues comprise 86% of the fatty acids (C₁₆; C₁₈; C₁₉; C₂₁; C₂₄; C₂₆), 83% of the primary alcohols (C₂₄; C₂₆; C₂₈; C₃₀; C₃₂; C₃₄) and 88% of the esters (C₃₆; C₃₈; C₄₀; C₄₁; C₄₂; C₄₄). Eleven major homologues amount only to 62% of the total hydrocarbons (C₁₆; C₁₇; C₁₈; C₂₀; C₂₆; C₂₇; C₂₉; C₃₀; C₃₁; C₃₂; C₃₃). Variability in the composition of soluble cuticular lipids between years was much smaller than variability of water permeability and, therefore, no relation between composition of soluble cuticular lipids and water permeability could be found. It is suggested that this may be due to the fact that the lipid composition observed represents the averages of 20 to 30 membranes analyzed so that differences between individual membranes may have been leveled out.Abbreviations CM cuticular membranes - MX polymer matrix - P_d permeability coefficient for diffusion of water - SCL soluble cuticular lipids - MES morpholinoethane sulphonic acid     

Determinants of serum levels of surfactant proteins A and B and Clara cell protein CC16

Increased leakage of surfactant proteins A and B (SP-A and SP-B) and Clara cell secretory protein (CC16) from the air spaces into the circulation occurs in a range of respiratory conditions. However, circulating levels depend not only on the rate of entry into the circulation, but also on the rate of clearance. In order to clarify the role of the kidney in the clearance of these proteins, serum levels were related to markers of glomerular filtration in 54 non-smoking patients with varying degrees of renal dysfunction, none of whom had respiratory disease or were receiving dialysis at the time of sampling. Serum SP-A was related to SP-B (r=0.53, p<0.001) and to CC16 (r=0.33, p<0.02). Similarly, SP-B was related to CC16 (r=0.39, p<0.004). Stepwise multiple linear regression analysis suggested that serum SP-A and SP-B are influenced by age (～20 and ～25% of variance, respectively), whereas CC16 is determined by renal function and, to a lesser extent, by body weight (～63% of variance in total). We conclude that CC16 is cleared from blood by the renal route, whereas SP-A and SP-B are not. Serum SP-A and SP-B are influenced by age, which we speculate reflects increased damage to the alveolocapillary barrier.     

Regulation of nitrate reductase in detached oat leaves by light and oxygen

Regulation of nitrate reductase (NR, EC 1.6.6.1) by oxygen concentration and light was studied in segments of oat ( Avena sativa L. cv. Suregrain) leaves, using the in vivo nitrate reductase assay. The activity of NR decreased after excision in either light or darkness; the addition of cycloheximide prevented this decrease. Treatments that increased tissue permeability (anoxia, Triton X-100) also increased NR activity. There was in general less NR activity in the light than in the dark and also less under aerobic (21–100% O₂) than under anaerobic (0.3% O₂) conditions. Treatments with antioxidants improved the activity in the light, but only at high O₂ levels (21–100% O₂).
The results suggest that NR may be regulated by inhibitory proteins synthesized in either light or darkness, by permeability changes and by light-induced oxidations that occur when O₂ is present. Oxygen may control the activity by stimulating the synthesis of inhibitory proteins in the light and in the dark and by promoting oxidation of SH-groups in the light.     

Metalloendopeptidases EC 3.4.24.15 and EC 3.4.24.16: potential roles in vascular physiology

Summary The zinc metalloendopeptidases EC 3.4.24.15 (EP 24.15) and EC 3.4.24.16 (EP 24.16) are closely related ubiquitous enzymes, which have well-defined in vitro activities in generation and degradation of a range of specific peptide targets. Despite this, little is known regarding their roles in whole animal physiology. One of the peptides degraded by these enzymes in vitro is bradykinin, a mediator with potent effects on the vasculature at both systemic and local levels. This review summarises the work that has examined the role of EP 24.15/24.16 in regulation of the vascular effects of bradykinin in vivo. This work was made possible by the development of a specific stable inhibitor of these enzymes, JA-2. Use of this inhibitor has shown that EP 24.15/24.16 are capable of regulating responses induced by exogenous bradykinin. This effect was observed at a systemic level with an increase in the hypotensive effect of intravenous bradykinin. Further work is required to determine whether these enzymes also regulate bradykinin produced endogenously.     

Comparative study on the properties of saturated phosphatidylethanolamine and phosphatidylcholine bilayers: Barrier characteristics and susceptibility to phospholipase A2 degradation

Comparative studies on bilayer systems of saturated phosphatidylcholines and phosphatidylethanolamines revealed a maximum in ionic permeability in phosphatidylcholine bilayers at the temperature of the gel to liquid-crystalline phase transition but such an increase in permeability was not detectable in bilayers of phosphatidylethanolamine. Furthermore, it was found that at the phase transition temperature the phosphatidylcholine bilayers are subject to rapid hydrolysis by pancreatic phospholipase A₂ whereas phosphatidylethanolamine bilayers are not. These differences are discussed in view of detailed information on the molecular organization in the gel and liquid crystalline phases of the two phospholipid classes.     

Operational patterns affecting lactic acid production in ultrafiltration cell recycle bioreactor

Lactic acid production with cell recycling on an ultrafiltration tubular membrane reactor was studied; higher lactic acid concentrations as well as productivities were obtained under long-term fermentations compared with other high cell density systems. Different operational conditions, namely dilution rates and start-up modes, were assessed. Performances were very different at the three different dilution rates tested (D = 0.20 h(-1), D = 0.40 h(-1), or D = 0.58 h(-1)). The different behaviours are discussed and factors responsible for them are presented. The best way to operate for lactic acid production is chosen, the dilution rate of D = 0.40 h(-1) being the one providing the best overall performance. On the other hand, results show that of the two start-up modes tested, continuous start (membrane open) permits higher permeabilities throughout the operational runs than batch start (membrane closed). Operational stability was found to be directly associated with membranes that work at "steady state," the membrane permeability being kept around 15 L/m(2) h. Optimized cell bleed can improve time of operation if such membrane permeability can be maintained for a longer time. A comparison of results with those obtained in other lactic acid production systems is presented; such comparison shows that this tubular ultrafiltration membrane cell recycle reactor presents three important advantages: (1) concomitant lactic acid concentrations and productivities; (2) long periods of operation at reasonable permeabilities; and (3) good mechanical stability permitting the use of steam sterilization. (c) 1995 John Wiley & Sons, Inc.     

Effect of cholera toxin on rat intestinal permeability assessed with fluorescent dextran 3000

Abstract The effect of culture filtrate containing cholera toxin (CT) on rat intestinal permeability was studied using fluorescein isothiocyanate-labelled dextran 3000 (FITC-D3, M _r, 3000) as probe molecule. CT was given either perorally, via a gastric tube 90 min before, or locally in conjunction with the permeability measurement in the distal ileum. Compaired to the control animals, either mode of administration resulted in increased permeation of FITC-D3 from the intestine to portal blood. The effect of the local treatment was apparent after 5–10 min and prevailed during the 60-min measurement period. The results indicate that CT not only affects net water transport at the intestinal mucosa but also the passage of larger molecules across the intestinal wall.     

Lipopolysaccharide transport to the cell surface: biosynthesis and extraction from the inner membrane

The cell surface of most Gram-negative bacteria is covered with lipopolysaccharide (LPS). The network of charges and sugars provided by the dense packing of LPS molecules in the outer leaflet of the outer membrane interferes with the entry of hydrophobic compounds into the cell, including many antibiotics. In addition, LPS can be recognized by the immune system and plays a crucial role in many interactions between bacteria and their animal hosts. LPS is synthesized in the inner membrane of Gram-negative bacteria, so it must be transported across their cell envelope to assemble at the cell surface. Over the past two decades, much of the research on LPS biogenesis has focused on the discovery and understanding of Lpt, a multi-protein complex that spans the cell envelope and functions to transport LPS from the inner membrane to the outer membrane. This paper focuses on the early steps of the transport of LPS by the Lpt machinery: the extraction of LPS from the inner membrane. The accompanying paper (May JM, Sherman DJ, Simpson BW, Ruiz N, Kahne D. 2015 Phil. Trans. R. Soc. B 370, 20150027. (doi:10.1098/rstb.2015.0027)) describes the subsequent steps as LPS travels through the periplasm and the outer membrane to its final destination at the cell surface.     

Polyelectrolyte-coated microcapsules and their potential applications to biotechnology

Polyelectrolyte-coated microcapsules can be prepared by adsorption of polyions onto microcapsule surfaces in aqueous solutions under appropriate pH and ionic conditions. The resulting polyelectrolyte-coated microcapsules provide a promising tool for studying pH-induced configurational changes in polyions adsorbed onto hydrophobic membranes (capsule walls). An interesting application of polyelectrolyte-coated microcapsules is the pH-sensitive on/off control of microencapsulated enzyme reactions through alterations in the substrate permeability of the capsule wall by pH-conditioned configurational changes in the adsorbed polyion layer. This paper presents an overview of pH-induced conformational changes of polyelectrolytes in solutions, preparation of polyelectrolyte-coated microcapsules with an immobilized enzyme, and on/off control of the respective enzyme reactions by pH adjustment. This revised version was published online in July 2006 with corrections to the Cover Date.     

Hemolysis of human erythrocytes induced by melamine-cyanurate complex

Melamine is a widely-used chemical in industries. In recent years, melamine has been found to be involved in outbreaks of renal injury in infants and animals. Pathological studies indicated that the melamine-induced acute renal failure was related to the concurrence of melamine and other triazine analogs such as cyanuric acid. In the present study, human erythrocytes were used as an in vitro model to explore the cytotoxicity of melamine and its complex with cyanuric acid. The results demonstrated that mixing melamine and cyanuric acid resulted in the formation of insoluble particles and that the insoluble melamine-cyanurate complex induced membrane damages of human erythrocytes. The membrane damages included hemolysis, K⁺ leakage, alterations in cell shape and membrane fragility, and inhibition of enzymatic activity. By contrast, either melamine or cyanuric acid alone had no effect on erythrocyte membranes. The results of this study may provide a fresh insight into the melamine toxicology.