The effect of Ca

31P NMR spectra of phosphatidylcholine-cardiolipin mixed liposomes were obtained as a function of Ca++ and Zn++ concentration for different temperatures. The ions induce non lamellar phases in this model membrane and it was observed that Zn++ is a better promotor of isotropic and hexagonal H11 phases than Ca++. The NMR observations can be correlated to the fusogenic power of these ions

Destabilization Of A Model Membrane By A Predicted Fusion Peptide Of Fertilin Alpha

peer reviewedThe subunit a of the guinea pig fertilin (previously known as PH-30, an integral membrane protein involved in sperm-egg binding and fusion) is predicted to be a potential fusion protein.The structure of this putative fusion protein was analysed by molecular modeling and we have found a peptidic sequence of 17 residues (D83-P99) organized in helix that inserts obliquely in lipid phases. The effect of ths synthesized peptide was studied on a model membrane by 3lP NMR and light scattering. It appears to increase the size of lipid vesicles and induces structural odifications. We interpret these observations as a destabilization of the lipid organization by this peptide because of its tilted insertion in phospholipid layers. This destabilization could favor membrane fusion

13C nuclear magnetic resonance analysis of glucose and citrate end products in an ldhL-ldhD double-knockout strain of Lactobacillus plantarum.

We have examined the metabolic consequences of knocking out the two ldh genes in Lactobacillus plantarum using 13C nuclear magnetic resonance. Unlike its wild-type isogenic progenitor, which produced lactate as the major metabolite under all conditions tested, ldh null strain TF103 mainly produced acetoin. A variety of secondary end products were also found, including organic acids (acetate, succinate, pyruvate, and lactate), ethanol, 2,3-butanediol, and mannitol

Cloning, nucleotide sequence and expression in Escherichia coli of a lipase gene from Bacillus subtilis 168.

The gene coding for an extracellular lipase of Bacillus subtilis 168 was cloned and found to be expressed in Escherichia coli. Enzyme activity measurements showed no fatty acid chain length preference. A set of Tn5 insertions which inactivate the gene were localized and used to initiate its sequencing. The nucleotide sequence was determined on two independent clones expressed in E. coli. In one of these clones, the sequence revealed a frameshift, due to the presence of an additional adenine in the N-terminal region, which caused the interruption of the open reading frame, probably allowing translation to initiate at a second ATG codon. The sequence of the wild-type lip gene from B. subtilis was confirmed on the chromosomal fragment amplified by polymerase chain reaction (PCR). When compared to other lipases sequenced to date, the enzyme described here lacks the conserved pentapeptide Gly-X-Ser-X-Gly supposed to be essential for catalysis. However, alignments of several microbial lipase sequences suggest that the pentapeptide Ala-X-Ser-X-Gly present in the lipase B. subtilis may function as the catalytic site. Homologies were found in the N-terminal protein region with lipases from different Pseudomonas species. The predicted M(r) and isoelectric point for the mature protein are 19,348 and 9.7 respectively

Aminoglycoside Antibiotics Prevent The Formation Of Non-Bilayer Structures In Negatively-Charged Membranes. Comparative Studies Using Fusogenic (Bis(Beta-Diethylaminoethylether)Hexestrol) And Aggregating (Spermine) Agents

Aminoglycoside antibiotics cause aggregation but not fusion of negatively-charged liposomes at an extent proportional to their capacity to interact with acidic phospholipids (Van Bambeke et al., 1995, Eur. J. Pharmacol., 289, 321-333). To understand why aggregation is not followed by fusion, we have examined here the influence of two aminoglycosides with markedly different toxic potential (gentamicin > isepamicin) on lipid phase transition in negatively-charged liposomes using 31P-NMR spectroscopy, in comparison with spermine (an aggregating agent) and bis(beta-diethylaminoethylether)hexestrol or DEH (a fusogenic cationic amphiphile). Gentamicin, spermine, and, to a lesser extent, isepamicin inhibit the appearance of the isotropic signal seen upon warming of control liposomes and denoting the presence of mobile structures. This non-bilayer signal appeared most prominently when liposomes were incubated with DEH, a strong fusogenic agent. We conclude that aminoglycosides, like spermine, have the potential to prevent membrane fusion, by inhibiting the development of a critical change in membrane organization, which is associated with fusion. We suggest that this capacity could be a determinant in aminoglycoside toxicity

Passive diffusion of polymeric surfactants across lipid bilayers.

Self-assembling polymeric surfactant, mmePEG(750)P(CL-co-TMC) [monomethylether poly(ethylene glycol)(750)-poly(caprolactone-co-trimethylene carbonate)], increases drug solubility and crosses an enterocyte monolayer both in vitro and in vivo. The aims of the present work were to investigate whether mmePEG(750)P(CL-co-TMC) polymers can diffuse passively through lipid bilayer using parallel artificial membrane permeability assay (PAMPA) and affect membrane properties using liposomes as model. The mmePEG(750)P(CL-co-TMC) polymer was able to cross by passive diffusion an enterocyte-mimicking membrane in PAMPA at concentration which did not perturb membrane integrity. A weak rigidification associated with a low increase in permeability of liposomal lipid bilayers was observed. These data suggest that polymeric surfactants can cross the lipid membrane by passive diffusion and interact with lipid bilayers