Interaction of melittin with dimyristoyl phosphatidylcholine liposomes. Evidence for boundary lipid by raman spectroscopy

The interaction of melittin, a polypeptide consisting of 26 amino acid residues, with dimyristoyl phosphatidylcholine bilayers was investigated by vibrational Raman spectroscopy. Spectral peak height intensity ratios, involving vibrational transitions in both the 3000 cm^?1 acyl chain methylene carbon-hydrogen stretching mode region and the 1100 cm^?1 acyl chain carbon-carbon skeletal stretching mode interval, served as temperature profile indices for monitoring the bilayer order-disorder processes. For a lipid : melittin molar ratio of 14 : 1 two order-disorder transitions were observed. In comparison to a gel to liquid crystalline phase transition of 22.5°C for the pure lipid, the lower transition, exhibiting a 2°C width, is centered at 17°C and is associated with a depression of the main lipid phase transition of dimyristoyl phosphatidylcholine. The second thermal transition, displaying a 7°C interval, occurs at approx. 29°C and is associated with the melting behavior of approximately seven immobilized boundary lipids which surround the inserted hydrophobic segment of the polypeptide. For a lipid : melittin molar ratio of 10 : 1 two thermal transitions are also observed at 11 and 30°C. As before, they represent, respectively, the main gel to liquid crystalline phase transition and the melting behavior of approximately four boundary lipids attached to melittin. From these data alternative schemes are suggested for disposing the immobilized lipids around the hydrophobic portion of the polypeptide within the bilayer.     

Ultrastructural studies on early events in fertilization of the bivalveLaternula limicola

Summary Ultrastructural studies on sperm-egg interaction at the time of fertilization inLaternula limicola were performed. The temporary-acrosome did not change morphologically while the sperm passed through the egg investments. At the onset of sperm entrance into the egg, however, the temporary-acrosome and mitochondria were eliminated from the sperm. Afterwards the sperm was engulfed by the egg surface without membrane fusion of the gametes. After entry the sperm nucleus was surrounded by four membranes: the plasma membranes of the egg and of the sperm, and the membranes of the sperm nuclear envelope. As the sperm nucleus differentiated into the male pronucleus, the plasma membranes of both the sperm and egg were initially vesiculated, then dispersed into the egg cytoplasm. Finally, the sperm nuclear envelope changed into the male pronuclear membrane accompanying sperm chromatin dispersion.     

Isolation of a high molecular weight glycoconjugate derived from the surface of S purpuratus eggs that is implicated in sperm adhesion

Sea urchin sperm–egg adhesion is mediated by bindin, a sperm surface protein that has lectin-like activity. Bindin agglutinates eggs, and this interaction has been shown to be inhibited by glycopeptides released from the egg surface by protease treatment. In this study, we report the purification and properties of such an egg surface glycoconjugate that may be involved in sperm adhesion. The glycoconjugate was partially purified by gel filtration and affinity chromatography on bindin particles. Upon gel filtration on Sepharose CL 4-B, the glycoconjugate elutes near the void volume, suggesting that it has a molecular weight in excess of one million. In addition, we have found that the egg surface glycoconjugate agglutinates bindin particles, indicating that it is multivalent. Carbohydrate analysis indicates that the glycoconjugate is composed primarily of fucosc, xylose, galactose, and glucose. This purified egg surface component is the most potent inhibitor of bindin-mediated egg agglutination yet described.     

Surface charge of protoplasts and their significance in cell-cell interaction

-potential of mesophyll protoplasts of tobacco (Nicotiana tabacum L.), petunia (Petunia hybrida Hort.), turnip (Brassica rapa L.) and cowpea (Vigna unguiculata L. Walpers) was determined by use of a cell electrophoresis apparatus. All protoplasts examined showed a constant negative value of-10 to-35 mV. The addition of CaCl₂ nullified the -potential of tobacco protoplasts. This phenomenon is explained by DLVO theory of colloid science, which has been successfully applied to animal cells. Furthermore, positively charged polymers reversed the -potential to positive values. Treatment of the protoplast surface with several enzymes was carried out to characterize the chemical nature of suface charges. The removal of surface charges was most conspicuous by the treatment of acid phosphatase (EC 3.1.3.2), but did not occur upon treatment with -neuraminidase (EC 3.2.1.18) or Streptomyces griseus pronase. Thus a major part of the surface charge originates from the phosphate groups at the cell membrane. The significance of these studies for the properties of the protoplast surface in cell adhesion is discussed.     

Cyanide as a feeding stimulant for the southern army worm, Spodoptera eridania

ABSTRACT.

• 1 All instars of Spodoptera eridania larvae grow as well or better when cyanide is present in their diet as when it is absent. Concentrations up to 0.05% stimulate feeding in first to fourth instar larvae. Concentrations from 0.1% to 1.0% stimulate feeding in fifth and sixth instar larvae.
• 2 Three-day-old sixth instar larvae pre-exposed to cyanide are completely resistant to its acutely toxic effects, but previously unexposed larvae suffer reversible symptoms of poisoning when feeding on a diet containing 1.0% KCN.
• 3 A 1.0% dietary KCN exposure during the sixth instar reduces ecdysis to 17% adult emergence and completely inhibits oviposition.
• 4 Cyanide concentrations from 0.5% to 1.0% in the diet, although effecting increased growth rates, induce necrotic lesions in larval mid-gut epithelial cells.
• 5 Thiocyanate, one of the in vivo cyanide metabolites, at 0.5% in the diet reduces pupation to 23%, delays and reduces adult emergence to 20% and inhibits oviposition.
• 6 The preferred host plant of S.eridania is the lima bean, Phaseolus lunatus, probably due to its content of the cyanogenic glycoside linamarin. Dietary valine has no effect on the southern armyworm feeding and growth behaviour (Long & Brattsten, 1982) but dietary cyanide does. The lima bean is known to contain up to 31 ppm cyanide in some varieties.

     

Characteristics of microsomal reduction of benzo[a]pyrene 4,5-oxide

NADPH-reduction of benzo[a]pyrene 4,5-oxide (BP-4,5-oxide) to BP required four components from rat liver: cytochrome P-450, NADPH cytochrome P-450 reductase, phosphatidylcholine and a soluble, heat-sensitive factor which was present in 105 000 × g supernatant and was also released from microsomes by sonication. The requirement for this factor contrasts with recently reported results from Sugiura et al. (Cancer Res., 40 (1980) 2910). Oxide-reduction was 40 times faster under anaerobic conditions, but oxygen did not affect the stimulation factor. This stimulation was highest (× 15) at low concentrations of microsomal protein (<0.1 mg/ml) and was almost absent at high concentrations of microsomal protein (>1 mg/ml). Oxide-reduction activity was proportional to microsomal protein concentration in the presence of added 105 000 × g supernatant, but for microsomes alone (>0.1 mg/ml) exhibited a parallel plot with an intercept at 0.08 mg/ml microsomal protein. Stimulation was highest at high concentrations of BP-4,5-oxide and a linear plot of V⁻¹ vs. [BP-4,5-oxide]⁻¹ was only obtained in the presence of 105 000 × g supernatant (K_m = 3 μM, V_max = 3.3 nmol/mg/min). Microsomal hydration of BP-4,5-oxide (inhibited in reductase assays) was unaffected by 105 000 × g supernatant, suggesting that stimulation of oxide-reduction did not derive from solubilization of BP-4,5-oxide. Stimulation was observed in the initial rate of reaction and was independent of incubation time. Inhibition of lipid peroxidation, removal of peroxides and deoxygenation were all excluded as explanations of the stimulatory effect.     

Intertidal distribution of infauna in a central California lagoon: the role of seasonal blooms of macroalgae

This study examined the roles of seasonal blooms of green algae, Ulva expansa (Setchell) Setchell et Gardner, and biotic disturbance by burrowing ghost shrimp, Callianassa gigas Dana, and foraging rays, on the intertidal distributions of a phoronid, Phoronopsis viridis Hilton, and a tellinid bivalve, Macoma nasuta (Conrad). Algal removal experiments in 1984 and 1986 demonstrated that heavy seasonal algal cover in the lower zone significantly reduced the abundances of both Phoronopsis and Macoma. Growth of Macoma transplanted into the algal zone was significantly lower in plots with algal cover than in plots regularly cleared of algae. Algal cover did not significantly affect early recruitment of either Phoronopsis or Macoma. Neither ghost shrimp nor rays appeared to reduce the abundances of phoronids or clams, although ray disturbance did result in a significant increase in the proportion of phoronids regenerating dorsal body parts. These results indicate that seasonal algal blooms are capable of producing discrete patterns of infaunal distribution in intertidal sedimentary habitats.     

Sensory interaction during trap-finding by female onion flies: implications for ovipositional host-plant finding

Using various three-dimensional traps alone and in combination with the onion volatile, dipropyl-disulphide (Pr₂S₂), we found that visual behaviour of female onion flies, Delia antiqua (Meigen), varied with the visual context (background composition and trap spacing) in which traps were presented and the females' reproductive state (mated vs. unmated). Against a background of real onions, females alighted more frequently on spherical than cylindrical traps, and white than green spheres, but females responded equally to white and green cylinders. In an onion field, baiting traps with Pr₂S₂ significantly increased female response to white over green traps, but had no influence on their response to trap shape. When traps were spaced 10 m apart and against a background of bare soil, females orienting to Pr₂S₂ baits alighted more frequently on vertical than horizontal traps, but shape and spectral reflectance were insignificant. However, when traps were spaced 0.25 m apart, females orienting to Pr₂S₂ baits alighted more frequently on cylinders than spheres. Mated females alighted more frequently on green than white cylinders, but unmated females responded to cylinders independent of spectral reflectance. When located 20 m downwind from Pr₂S₂ baits, mated females alighted on green cylinders significantly more often than unmated females. Response to traps mimicking onion plants suggests that ovipositional host-finding in female onion flies is dominated by olfactory responses at long range (several metres) and by visual cues at short-range (ca. 1 m). The view that host location by female onion flies is a hierarchical response pattern mediated by multiple sensory modalities and modified by resource level (habitat) and reproductive status, is discussed.     

Foraging behavior of specialist and generalist caterpillars on plantain (Plantago lanceolata) altered by predatory stinkbugs

Summary To examine the effects of predators and plant genotype on the behavior, patterns of herbivory, growth and survivorship of caterpillars, we used an experimental garden in which we contrasted two hostplant genotypes of plantain (Plantago lanceolata), two kinds of herbivores (specialist Junonia coenia vs. generalist Pyrrharctia isabella) and two levels of caterpillar predation (with and without Podisus maculiventris stinkbugs). Each of the replicate plots per treatment contained two plants of the same genotype. The stinkbugs reduced the survivorship of the specialist caterpillars but not that of the generalists, which reflects the differences in predatoravoidance behaviors of these species. Nonetheless, the stinkbugs influenced the behavior of both caterpillar species. When stinkbugs were present, both specialist and generalist caterpillars were less likely to be found on the plant upon which they were initially placed (=initial plant), and they were more likely to be off both plants within the plot than larvae in the absence of predators. Consequently in the presence of the stinkbug predators, the proportion of the initial plants consumed was less than in the absence of the predators. Plant genotype influenced plant size and the proportion of individual plants eaten, but it did not affect larval location on the plots. Neither presence of predators nor plant genotype had an effect on relative growth rate of the caterpillars.