Cercospora beticola toxins. Part VI: preliminary studies of protonation and complexation equilibria

The biological activity of Cercospora beticola toxins might be enhanced by the complex formation with magnesium. Therefore, protonation and complexation equilibria of beticolins were studied. Beticolins carry three dissociable functions (H3B) two of which dissociate at a physiological pH. In the presence of magnesium, the neutralisation and protonation curves provide evidence for the formation of complexes. At physiological pH, the uncharged complex, Mg2H2B2, is the predominant form. The nonionised forms of free beticolin-1 and -2 fluoresce in a 50% dioxan-water solution and their emission maxima shift to higher wavelengths in water. The dianion HB(2-) is non-fluorescent both in water and in less polar media. The formation of the Mg2H2B2 complex which strongly fluoresces in nonpolar media is confirmed by a marked increase in fluorescence at 520 nm and by a shift of the excitation maximum.     

Conformational transitions of human alpha-1 fetoprotein and serum albumin at acid and alkaline pH

Conformational transitions of HAFP in the pH-range 2-12 were studied by fluorescence spectroscopy, fluorescence polarization measurements, circular dichroism and hydrophobic chromatography in order to compare molecular architecture of HAFP and that of human serum albumin. It was found that HAFP has a remarkably hydrophilic exposed molecular surface at neutral pH and possesses extensive hydrophobic binding sites located in crevices. Conformational changes occur in HAFP in the acid and alkaline pH regions; extensive hydrophobic areas in HAFP are exposed by both acid and alkaline transitions. The alpha-helix contents of HAFP were determined as 67% at pH 7.6, 47% at pH 2.11.     

A protein with lectin activity in penetration glands of Diplostomum pseudospathaceum cercariae

Homogenates of Diplostomum pseudospathaceum cercariae agglutinated mouse erythrocytes. The haemagglutination could be inhibited by certain glycoconjugates containing beta-1,3- and beta-1,4-glycan chains and also by some simple saccharides. The most potent inhibitors were heparin and some other glycosaminoglycans, bacterial lipopolysaccharides, laminarin (a beta-1,3-glucan) and lactulose. After electrophoresis of cercarial proteins, a dominant double band appeared in the 22-24 kDa region of gels. On blots, this protein bound labelled laminarin and it was also one of the few proteins recognised by mouse antibodies raised against cercarial haemagglutinins. In addition, mouse polyclonal antibodies against the beta-1,3-glucan-binding protein bound exclusively to the 22-24 kDa region on Western blots. Histochemistry revealed strong binding of labelled laminarin to cercarial penetration glands; this reaction was fully blocked by unlabelled laminarin. Other labelled glycoconjugates such as heparin, hyaluronic acid and a bacterial lipopolysaccharide also bound to the glands. Immunohistochemistry confirmed the localisation of the beta-1,3-glucan-binding protein in penetration glands. Reaction of the cercarial protein with immunoglobulins from non-immunised mice was observed on both nitrocellulose membranes and histological sections; this could be blocked by laminarin in incubation buffers. We consider the cercarial haemagglutinin to be a lectin which is identical with the 22-24 kDa beta-1,3-glucan-binding protein. According to the binding specificity and localisation we speculate on a role of this lectin in cercarial penetration into the host, probably as a tissue recognition or antibody rendering factor.     

Filling of a wetland (Seine estuary,France): natural eutrophication or anthropogenic process? A sedimentological and geochemical study of wetland organic sediments

Hydrobiologia - For over a century the Seine estuary has been highly affected by human activities, resulting in a reduction of the surface of wetland habitat. Several ponds of the Vernier Marsh,...     

Preliminary Estimation of the Factors Influencing the Distribution of the Midlittoral Crab Portumnus lysianassa (Herbst, 1796)

In order to acquire information on the factors influencing the distribution of the Mediterranean endemic species Portumnus lysianassa (Herbst, 1796), which lives in the soft substratum midlittoral zone, 83 stations were selected along almost the entire Greek coast. In each sampling station, dredging was carried out, just above the rise of the surf zone, and sediment samples were taken with a core sampler. Two faunal samples were also taken by means of a quadrat from the lower midlittoral zone. The preliminary results of this study show that: P. lysianassa prefers to burrow in the rise of the surf zone; wherever the sediment becomes very coarse or very fine the crab populations decline; there is a correlation between the population abundance of the midlittoral bivalve Donacilla cornea (Poli, 1795) and P. lysianassa, and, moreover, this crab species is related to the composition of the midlittoral assemblage; also, P. lysianassa abundance is negatively correlated with the organic matter content of the sediment; in very exposed areas, D. cornea can be replaced or co-exist with the infralittoral species Donax trunculus (Linnaeus, 1758), and, in these cases, P. lysianassa can be replaced by the closely related infralittoral species Portumnus latipes (Pennant, 1777); when low temperatures or intensive wave action, as well as disturbance caused by swimmers in summer prevail, the population of this crab descends in the upper infralittoral zone.     

Ergosterol elicits oxidative burst in tobacco cells via phospholipase A2 and protein kinase C signal pathway.

Ergosterol, a typical fungal sterol, induced in tobacco (Nicotiana tabacum L. cv. Xanthi) suspension cells the synthesis of reactive oxygen species and alkalization of the external medium that are dependent on the mobilization of calcium from internal stores. We used specific inhibitors to elucidate the signal pathway triggered by ergosterol compared with cryptogein, a proteinaceous elicitor of Phytophthora cryptogea. Herbimycin A and genistein, inhibitors of tyrosine protein kinases, had no effect on the oxidative burst and pH changes induced by both elicitors. Similarly, H-89, an inhibitor of protein kinase A, had no effect on the induction of these defense reactions. However, the response to both elicitors was completely blocked by NPC-15437, a specific inhibitor of animal protein kinase C (PKC). The responses induced by cryptogein but not those induced by ergosterol were inhibited by U73122 and neomycin, inhibitors of phospholipase C (PLC). On the other hand, the activity of phospholipase A2 (PLA2) measured using a fluorogenic substrate was stimulated by ergosterol and not by cholesterol and cryptogein. A specific inhibitor of PLA2, arachidonic acid trifluoromethyl ketone (AACOCF3), inhibited the pathway stimulated by ergosterol but not that induced by cryptogein. These results suggest that the cryptogein-induced signal pathway leading to the oxidative burst and DeltapH changes includes PLC and PKC, whereas this response induced by ergosterol includes PLA2 and PKC.     

Diet composition of the seahorses, Hippocampus guttulatus Cuvier, 1829 and Hippocampus hippocampus (L., 1758) (Teleostei, Syngnathidae) in the Aegean Sea

The diet composition of the European seahorses, Hippocampus guttulatus and Hippocampus hippocampus was determined based on the analysis of 279 and 19 specimens, respectively, collected in the Aegean Sea. The diet of both species was mainly based on Crustacea, with Amphipoda, Anomura Decapoda and Mysidacea being the dominant prey categories. ANOSIM analyses, however, indicated statistically significant differences in the diet of the two species as well as differences in the diet composition of non-brooding males, brooding males and females within each species. In H. guttulatus , stomach fullness percentages and vacuity coefficient values indicated that female individuals seem to have a higher feeding activity in relation to males.     

Bifidobacteria-mediated immune system imprinting early in life

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