Physicochemical characterisation of four peptide sequences related to thrombospondin-1B

Thrombospondin-1 (TSP-1) is a protein involved in angiogenesis and tumor metastasis. In a previous study, a tridecapeptide sequence of TSP-1B [KRFKQDGGWSHWG] was synthesized and its biological activity was determined as well as the activity of three related sequences TSPB-(E), TSPB-(S), and TSPB-(Abu)(6). These peptides were tested for activity on the cell growth of three human carcinoma cells lines and only TSPB-(Abu)(6) increased proliferation of MCF7 and HT-29. The main aim of this study was to perform physicochemical measurements, in a comparative way, to determine if the differences in activity could be related to physicochemical properties. Peptides were characterised by HPLC capacity factors, UV, fluorescence, and CD spectra (either in buffer solution or in the presence of lipid vesicles), surface activity, and aggregation. Moreover, the interaction of these peptides with phospholipids was determined through their penetration in monolayers of DPPC, PG, or PS as well as their miscibility in mixed monolayers. Besides, using liposomes as model membranes, the affinity of these peptides for phosphatidylcholine was measured with vesicles labeled with fluorescent markers (TMA-DPH, laurdan, pyrene). Results show that these molecules are highly hydrophilic and their surface activity is low. Mixed monolayers indicate that there is almost no miscibility. Besides, its presence does not modify noticeably the microviscosity of bilayers. Moreover, UV and fluorescence spectra of peptides were not affected by the presence of lipids in the media but CD spectra recorded in TFE/water (1/1) resulted in small changes for TSPB, TSPB-(E), and TSPB-(S) peptides. On the contrary CD spectra of TSPB-(Abu)(6) derivatives were clearly much more sensitive to the polarity of the environment. According to these data the biological activity of peptide with a cyclic aspartimide moiety at position 6 could be related to a specific conformational change in the peptide chain promoted by a hydrophobic membrane-like environment.     

On a family of connectives for fuzzy sets

In this paper we find the general solution of the functional equation $\text{S}{}^1\text{(T(x, y), T(x, N(y))) = x}$, where $\text{S}{}^1$ is a t-conorm, T is a t-norm and N is a strong negation on the unit interval. In particular the result yields a family of connectives for fuzzy sets.     

On Two Functional Equations Related to A Result of Grégoire De Saint Vincent

We give two characterizations of the exponential function by solving two functional equations related to some classical considerations made by Grégoire de Saint-Vincent in the 17th century.     

Acoustically induced potential dots in GaAs quantum wells

Dynamic dots (DDs) consisting of confined and mobile potentials are realized by the interference of orthogonal surface acoustic wave (SAW) beams in GaAs quantum wells. Photoluminescence spectroscopy reveals that the DDs are characterized by a peculiar distribution of strain and piezoelectric fields dictated by the lattice symmetry, which is quite different from the one induced by a single SAW. We demonstrate the unique ability of DDs to control the flow of photogenerated electron-hole pairs and of photons by realizing an electronic switch based on SAWs.     

Action de l'AMP-c sur les monocouches mixtes de céphaéline-albumine d'œuf

Résumé En vue de vérifier si l'AMP-cyclique produit une action expansive lorsqu'il agit sur les monocouches de lipoprotéines mixtes ces monocouches insolubles ont été préparées avec de la céphaéline et de l'albumine dóeuf.Ces monocouches ont montré une bonne miscibilité entre les deux composants, et seules de faibles actions réciproques ont été observées.La pénétration de l'AMP-cyclique dans ces monocouches mixtes produit un effet expansif appréciable, son action atteignant le niveau maximal lorsque la concentration de l'AMP-cyclique dans la sous-phase est de 10^–6 M (concentration normale de la cellule).Un effet similaire sur les membranes mixtes de lipoprotéines de la paroi cellulaire est attribué a l'AMP-cyclique.

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With a view to checking whether cyclic-AMP produces an expansive action when acting on mixed lipoprotein monolayers, such insoluble monolayers were prepared with cephalin and egg albumin. These layers showed a good miscibility between the two components, with only weak interactions being observed.The penetration of cyclic-AMP in these mixed monolayers produces an appreciable expansive effect, its action reaching a maximum level when the cyclic-AMP concentration in the subphase is 10^–6 M (standard cell concentration).A similar effect on the lipoprotein mixed membranes of the cell wall is attributed to cyclic-AMP.

Directeur du Département: Prof. Dr. Serafín Garcia Fernández     

Membrane association and contact formation by a synthetic analogue of polymyxin B and its fluorescent derivatives

sP-B is a synthetic analogue of the natural lipopeptide antibiotic polymyxin B (PxB) that maintains the ability of the parent compound to form vesicle-vesicle contacts and induce lipid exchange. Exchange is selective, and only monoanionic phospholipids such as 1-palmitoyl-2-oleoyl-glycero-sn-3-phosphoglycerol (POPG) are transferred, whereas dianionic phospholipids such as 1-palmitoyl-2-oleoyl-glycero-sn-3-phosphate (POPA) are not, as shown by fluorescence experiments based on the excimer/monomer ratio of pyrene-labeled phospholipids. Synthetic fluorescent analogues of sP-B are used to investigate the peptide position and orientation in the intermembrane contacts: sP-Bw, an analogue that contains D-tryptophan (D-Trp) instead of the naturally occurring D-phenylalanine, and sP-Bpy, incorporating a pyrene group at the N-terminus. Tryptophan fluorescence, anisotropy, and quenching measurements performed with sP-Bw indicate that the peptide binds and inserts in anionic vesicles of POPG and POPA. However, significant differences are seen depending on the lipid composition, as also demonstrated by fluorescence resonance energy transfer (FRET) experiments from Trp to 7-nitro-2-1,3-benzoxadiazol (NBD) groups at the interface. Intermolecular FRET using sP-Bw as the donor and sP-Bpy as the acceptor indicates self-association of the peptide, possibly forming dimers, when bound to POPG vesicles at concentrations that induce the vesicle-vesicle contacts.