Effects of pH and deuterium oxide on the heat-inactivation temperature of chloroplasts

The inactivation temperature for Hill activity and for the long-lived delayed fluorescence of isolated Pisum sativum L. chloroplasts was found to depend on pH, the maximal value being in the pH region 5–7. Salts increase the inactivation temperature by 4–7°C. Effects of D₂O and some other substances that modify the thermostability of chloroplasts are dependent on pH. It is concluded that thermal denaturation of proteins is the most probable mechanism for heat inactivation of chloroplasts.Abbreviations Hepes 4-(2-hydroxymethyl)-1-piperazineethane sulfonic acid - Tris 2-amino-2-(hydroxymethyl)-1,3-propanediol     

Yeast β(1-3),(1-6)-d-glucan films: Preparation and characterization of some structural and physical properties

Cell wall polysaccharide suspensions (mainly β-glucan) was isolated from baker's yeasts (Saccharomyces cerevisiae) and used for the preparation of films. Glycerol was added as a plasticizer. Purity and composition of the films were tested by elemental analysis, enzymatic assay of α- and β-glucans, monosaccharide composition analysis (total hydrolysis, HPAEC) and vibration spectroscopy (FTIR, FT Raman). Surface properties and the degree and type of crystallinity, together with ageing effects, were estimated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD). Mechanical and thermal properties were characterized by tensile tests and difference scanning calorimetry (DSC), respectively. The prepared films were water insoluble, compact, non-porous, exhibit no pronounced crystallinity and consist of granular-like and fibre microstructures, which could be assigned as cell wall residues and released polysaccharide macromolecules. Certain structural changes in the film surface during one-year shelf storage can be related to reorientation and decomposition of surface macromolecules due to reaction with the ambient atmosphere, rather than to crystallization phenomena.     

Composition and characteristics ofCandida albicans cells differing in resistance to polyene antibiotics

Development of resistance to polyene antibiotics in a highly resistantCandida albicans strain was shown to be accompanied by the complete loss of the ability to synthesize ergosterol and the substitution of other sterol components as well as by higher amounts of free fatty acids. No significant differences in lipid and protein composition have been noted between slightly resistant cultures ofC. albicans and initially susceptible ones. Sterols of resistant cultures (added in the solution and incorporated in the composition of native membranes and liposomes) have the same affinity for polyene antibiotics as do sterols of a sensitive strain. It was found that the resistance of the slightly resistantC. albicans strain did not depend on the cell wall. The ability of some detergents to reduce resistance to polyene antibiotics was shown.     

Cariniferosides A–F and other steroidal biglycosides from the starfish Asteropsis carinifera

Six new steroidal biglycosides, cariniferosides A–F (1–6), were isolated along with six previously known glycosides, 7–12, from the alcoholic extract of the starfish Asteropsis carinifera. The structures of 1–6 were determined by extensive NMR and ESIMS techniques. The isolated compounds did not show any apparent cytotoxicity in cancer cell lines HCT-116, RPMI-7951, and T-47D, but sulfated compounds 6, 11, and 12 demonstrated a significant inhibition of RPMI-7951 and T-47D cell colony formation in a soft agar clonogenic assay.     

The change in membrane phospholipid composition influences protein secretion and cell envelope biogenesis in Escherichia coli

Secretion of periplasmic alkaline phosphatase (PhoA) encoded by the gene constituent of plasmids and the peculiar properties of cell envelope biogenesis in Escherichia coli strains with controlled synthesis of individual membrane phospholipids have been studied. Alkaline phosphatase secretion across the cytoplasmic membrane declines, while secretion into the culture medium intensifies under changed metabolism. The composition of anionic membrane phospholipids changes due to inactivation of the pgsA gene or regulation of its expression by environmental factor, as well as in the absence of the pssA gene which is responsible for the synthesis of the precursor for zwitter-ionic phospholipid — phosphatidylethanolamine. This correlates with intensified secretion of exopolysaccharides and lower content of lipopolysaccharide and lipoprotein which are responsible for barrier properties of the outer membrane. The results suggest a possible coupling of protein secretion with biogenesis of cell envelope components at a level of phospholipid metabolism.