Interaction of C-phycocyanin with lipid monolayers under nitrogen and in the presence of air

The surface interaction of C-phycocyanin with lipids was studied using the monolayer technique. The surface activity of the protein was found to be higher at the lipid-water interface than at the nitrogen-water interface, particularly at high surface pressures of the lipid monolayer. The maximum initial surface pressures beyond which phycocyanin could not penetrate the dipalmitoylphosphatidylcholine and monogalactosyldiglycerol monolayers were 27 and 30 mN m-1, respectively. Below these values the protein demonstrated preferential interaction with the monogalactosyldiglycerol monolayer. The surface properties of the unfolded protein at pH 2.5 at the lipid-water interface were compared with those of the protein at pH 7.0. Higher affinity of the three-dimensional structure of the protein to lipid monolayers was observed, in particular by high subphase protein concentration. When the lipid films were subjected to oxidation stress by exposure to air, the surface properties of C-phycocyanin and dipalmitoylphosphatidylcholine were not greatly affected but the surface activity of monogalactosyldiacylglycerol was reduced dramatically by autoxidation. The oxidation of monogalactosyldiacylglycerol could not be prevented by the introduction of C-phycocyanin molecules at the lipid-water interface.     

Slow heat rate increases yeast thermotolerance by maintaining plasma membrane integrity.

Thermal resistance of Saccharomyces cerevisiae was found to be drastically dependent on the kinetics of heat perturbation. Yeasts were found to be more resistant to a plateau of 1 h at 50 degrees C after a slope of temperature increase (slow and linear temperature increments) than after a shock (sudden temperature change). Thermotolerance was mainly acquired between 40-50 degrees C during a heat slope, i.e., above the maximal temperature of growth. The death of the yeasts subjected to a heat shock might be related to the loss of membrane integrity: intracellular contents extrusion, i.e., membrane permeabilization, was found to precede cell death. However, the permeabilization did not precede cell death during a heat slope and, therefore, membrane permeabilization was a consequence rather than a cause of cell death. During a slow temperature increase, yeasts which remain viable may have time to adapt their plasma membrane and thus maintain membrane integrity.     

A note on a modified membrane-Bovis agar for the enumeration of Streptococcus bovis by membrane filtration

The effect of dilution and temperature on the antibacterial properties of potassium sorbate was determined. The time taken to kill a standard inoculum of Escherichia coli was increased considerably after either dilution of the preservative or lowering of the temperature. The value for the concentration exponent, eta, was approximately 3 and that for the temperature coefficient, Q10, was 2.3.     

Effect of calcium on kinetic and structural aspects of dilution-induced micellar to lamellar phase transformation in phosphatidylcholine-cholate mixtures

Previously, we have shown [Almog, S., Kushnir, T., Nir, S., & Lichtenberg, D. (1986) Biochemistry 25, 2597-2605] that the distribution of cholate between phosphatidylcholine (PC) vesicles and aqueous media apparently obeys a single distribution coefficient, K. In PC-cholate mixed micellar systems, the monomer concentration does not rise much above the cholate's critical micelle concentration (cmc). Consequently, for vesicular systems, the cholate:PC molar ratio in the mixed aggregates (Re) is given by Re = [cholate]/([PC] + 1/K) whereas for mixed micellar systems Re = ([cholate] - cmc)/[PC]. Dilution of mixed micellar systems results in a decrease of Re, due to an increase in the fraction of monomeric PC. If the decrease in Re is to values lower than 0.3, micellar to lamellar transformation occurs. This process involves a sequence of three steps, namely, micellar equilibration followed by vesiculation and subsequent vesicle size growth via a lipid transfer mechanism. The ultimate size of the resultant vesicles is an increasing function of Re. This work is devoted to the effect of calcium on the dilution-induced vesicle formation. Its major findings and conclusions are as follows: (i) Calcium reduces the cmc of the detergent and raises its distribution coefficient between PC vesicles and the aqueous medium. Thus, for any given cholate and PC concentrations, calcium causes an increase of Re. (ii) The rate of all the steps which ultimately lead to an apparent equilibrium vesicle size distribution increases dramatically with increasing calcium concentration. Thus, equilibration is attained in seconds to minutes rather than many hours required in the absence of calcium.(ABSTRACT TRUNCATED AT 250 WORDS)     

Precipitation of calcium palmitate from bile salt-containing dispersions

Addition of calcium chloride to mixed micellar systems composed of sodium salts of palmitic acid and high concentrations of different bile acids results in precipitation of Ca(palmitate)2 only when the palmitate concentration exceeds a critical value, which is dependent on the concentrations of Ca2+, Na+ and bile salt, and on the type of bile salt used. All these dependencies, as well as the complex and interrelated effects of the various parameters on the kinetics of Ca(palmitate)2 precipitation are consistent with the following mechanism: (i) calcium binds to palmitate-bile salt mixed micelles and promotes their aggregation, at a rate governed by the concentration ratio between bound calcium and micelles (here denoted "binding ratio"). (ii) Ca(palmitate)2 precipitation occurs within the aggregate of micelles only if those micelles include sufficient amounts of Ca2+ and palmitate to allow for the formation of large enough crystal units of Ca(palmitate)2 which can serve as nucleation "seeds". Both the concentrations of micelles and Na+ have dual effects on the rate of precipitation. Increasing micelle concentration, by itself, accelerates aggregation but at the same time leads to a decrease of the binding ratio, thus reducing the rate of precipitation. Na+ which reduces the binding ratio through competitive binding also reduces the surface charge, thus assisting micelle aggregation. Our model also explains the facilitation of precipitation observed when phosphatidylcholine is contained in the palmitate-bile salt mixed micelles and the inhibitory effect of the water soluble bovine serum albumin.     

Hydrolysis of phosphatidylcholine in phosphatidylcholine-cholate mixtures by porcine pancreatic phospholipase A2

Pancreatic phospholipase A2 (PLA2)-catalyzed hydrolysis of egg yolk phosphatidylcholine (PC) in mixed PC-cholate systems depends upon composition, structure, and size of the mixed aggregates. The hydrolysis of PC-cholate-mixed micelles made of an equal number of PC and cholate molecules is consistent with a Km of about 1 mM and a turnover number of about 120 s-1. Increasing the cholate/PC ratio in the micelles results in a decreased initial velocity. Hydrolysis of cholate-containing unilamellar vesicles is very sensitive to the ratio of cholate to PC in the vesicles. The hydrolysis of vesicles with an effective cholate/PC ratio greater than 0.27 is similar to that of the mixed micelles. The time course of hydrolysis of vesicles with lower effective ratios is similar to that exhibited by pure dipalmitoyl-phosphatidylcholine (DPPC) large unilamellar vesicles in the thermotropic phase transition region. In the latter two cases, the rate of hydrolysis increases with time until substrate depletion becomes significant. The reaction can be divided phenomenologically into two phases: a latency phase where the amount of product formed is a square function of time (P(t) = At2) and a phase distinguished by a sudden increase in activity. The parameter A, which describes the activation rate of the enzyme during the initial phase in a quantitative fashion, increases with increasing [PLA2], decreasing [PC], decreasing vesicle size, and increasing relative cholate content of the vesicles. The effect of [PLA2] and [PC] on the hydrolysis reaction is similar to that found with pure DPPC unilamellar vesicles in their thermotropic phase transition region. The effect of cholate on the hydrolysis reaction is similar to that of temperature variation within the phase transition of temperature variation within the phase transition of DPPC. These results are consistent with our previously proposed model, which postulates that activation of PLA2 involves dimerization of the enzyme on the substrate surface and that the rate of activation is directly proportional to the magnitude of lipid structural fluctuations. It is suggested that large structural fluctuations, which exist in the pure lipid system in the phase transition range, are introduced into liquid crystalline vesicles by the presence of cholate and thus promote activation of the enzyme.     

Endotheliochorial Placentation in a Pangolin,Manis tetradactyla

The placenta of a pangolin, Manis tetradactyla, was examined grossly and histologically. The placenta was arranged in longitudinal bands of 2–3 mm width. Microscopically there was a deep labyrinth and an underlying layer of distended endometrial glands. A narrow junctional zone was present containing syncytiotrophoblast. Thoughout the labyrinth cytotrophoblast and syncytiotrophoblast were observed in contact with maternal capillaries. The placentation was considered to be endotheliochorial in type.     

Phytoplankton biomass and production in shelf waters off NW Spain: spatial and seasonal variability in relation to upwelling

Summary Chlorophyll-a and primary production on the euphotic zone of the N-NW Spanish shelf were studied at 125 stations between 1984 and 1992. Three geographic areas (Cantabrian Sea, Rías Altas and Was Baixas), three bathymetric ranges (20 to 60 m, 60 to 150 m and stations deeper than 200 m), and four oceanographic stages (spring and autumn blooms, summer upwelling, summer stratification and winter mixing) were considered. One of the major sources of variability of chlorophyll and production data was season. Bloom and summer upwelling stages have equivalent mean and maximum values. Average chlorophyll-a concentrations approximately doubled in every step of the increasing productivity sequence: winter mixing — summer stratification — high productivity (upwelling and bloom) stages. Average primary production rates increased only 60% in the described sequence. Mean (± sd) values of chlorophyll-a and primary production rates during the high productivity stages were 59.7 ± 39.5 mg Chl-a m^–2 and 86.9 ± 44.0 mg C m^–2 h^–1, respectively. Significant differences in both chlorophyll and primary production resulted between geographic areas in most stages. Only 27 stations showed the effects of the summer upwelling that affected coastal areas in the Cantabrian Sea and Rías Baixas shelf, but also shelf-break stations in the Rías Altas area. The Rías Baixas area had lower chlorophyll than both the Rías Altas and the Cantabrian Sea areas during spring and autumn blooms, but higher during summer upwelling events. On the contrary, primary production rates were higher in the Rías Baixas area during blooms in spring and autumn. Mid-shelf areas showed the highest chlorophyll concentrations during high productivity stages, probably due to the existence of frontal zones in all geographic areas considered. The estimated phytoplankton growth rates were comparable to those of other coastal upwelling systems, with average values lower than the maximum potential growth rates. Doubling rates for upwelling and stratification stages in the northern and Rías Altas shelf areas were equivalent, despite larger biomass accumulations during upwelling events. Low turnover rates of the existing biomass in the Rías Baixas shelf in upwelling stages suggests that the accumulation of phytoplankton was due mainly to the export from the highly productive rías, while the contribution of in situ production to these accumulations was relatively lower.     

Candida albicans stress mannoproteins expression in superficial and systemic candidiasis

The presence of heat shock mannoproteins (HSMPs) reactive with sIgA was demonstrated in several C. albicans strains. The subculture of the C. albicans isolated from mucosal surfaces on Sabouraud's dextrose agar at 25 °C switched off the HSMP expression. A re-expression of the HSMPs was obtained in the same medium by shifting the temperature of incubation to 37 °C. However, expression of HSMPs in two strains isolated from deep infections was maintained during several subcultures on Sabouraud's dextrose agar at 25 °C. A glycoprotein of 200 kDa seemed to be the main HSMP reacting with vaginal sIgA. The data presented in this study suggest that factors other than temperature can influence the expression of C. albicans HSMPs and therefore these antigens should be referred as stress mannoproteins.Abbreviations HSMPs heat shock mannoproteins - MAb monoclonal antibody - sIgA secretory IgA