Ortho-aminobenzoic acid as a fluorescent probe for the interaction between peptides and micelles.

Ortho-aminobenzoic acid (o-Abz) has been used as a fluorescent probe in internally quenched fluorescent peptides for continuous protease assays. We investigated the fluorescent properties of the probe in order to verify if it can be used to monitor the interaction of peptides with micelles. Abz-aminoacyl-monomethyl amides (Abz-Xaa-NHCH(3), where Xaa=Arg, Phe, Leu and Glu) were synthesized.

DMPG gel-fluid thermal transition monitored by a phospholipid spin labeled at the acyl chain end.

Low ionic strength aqueous dispersion of dimyristoyl phosphatidylglycerol (DMPG) presents a rather peculiar gel-fluid thermal transition behavior. The lipid main phase transition occurs over a large temperature interval (ca. 17 degrees C), along which several calorimetric peaks are observed.

The peculiar thermo-structural behavior of the anionic lipid DMPG.

Aqueous dispersions of the anionic phospholipid dimyristoyl phosphatidylglycerol (DMPG), around 100 mM ionic strength, are known to exhibit a thermal behavior similar to that of the largely studied lipid dimyristoyl phosphatidylcholine (DMPC), which undergoes a gel to liquid crystalline phase transition at 23 degrees C, well characterized by differential scanning calorimetry (DSC), and other methods. However, at low ionic strength, DMPG has been shown to present a large gel-fluid transition region, ranging from 18 to 35 degrees C. This intermediate phase is optically transparent and characterized by a continuous change in membrane packing.

Ortho-aminobenzoic acid-labeled bradykinins in interaction with lipid vesicles: fluorescence study.

The peptide hormone bradykinin (BK) (Arg(1)-Pro(2)-Pro(3)-Gly(4)-Phe(5)-Ser(6)-Pro(7)-Phe(8)-Arg(9)) and its shorter homolog BK(1-5) (Arg(1)-Pro(2)-Pro(3)-Gly(4)-Phe(5)) were labeled with the extrinsic fluorescent probe ortho-aminobenzoic acid (Abz) bound to the N-terminal and amidated in the C-terminal carboxyl group (Abz-BK-NH(2) and Abz-BK(1-5)-NH(2)). The fragment des-Arg(9)-BK was synthesized with the Abz fluorescent probe attached to the 3-amino group of 2,3-amino propionic acid (DAP), which positioned the Abz group at the C-terminal side of BK sequence, constituting the peptide des-Arg(9)-BK-DAP(Abz)-NH(2). The spectral characteristics of the probe were similar in the three peptides, and their fluorescent properties were monitored to study the interaction of the peptides with anionic vesicles of dimyristoylphosphatidylglycerol (DMPG).

Role of soft and hard aggregates in the thermodynamics of lipid dispersions.

We study the thermodynamics of a two-dimensional polydisperse ideal gas model of different species of aggregates. We show that if these aggregates are distinguished not only by their sizes but also by their ability to display shape fluctuations, the system presents dominance of one or other species, depending on the temperature region. This result, which emerges solely from the statistics of the model in total absence of interaggregate interactions, describes well the observed temperature dependence of light scattering in dispersions of dimyristoyl phosphatidylglycerol, a negatively charged lipid.