Mechanism of Long-Chain Free Fatty Acid Protonation at the Membrane-Water Interface.

Long-chain free fatty acids (FFAs) play an important role in several physiological and pathological processes such as lipid fusion, adjustments of membrane permeability and fluidity, and the regulation of enzyme and protein activities. FFA-facilitated membrane proton transport (flip-flop) and FFA-dependent proton transport by membrane proteins (e.g.

The molecular mechanism behind reactive aldehyde action on transmembrane translocations of proton and potassium ions.

Membrane transporters are involved in enormous number of physiological and pathological processes. Under oxidative stress they become targets for reactive oxygen species and its derivatives which cause protein damage and/or influence protein function(s). The molecular mechanisms of this interaction are poorly understood.

Selective permeabilization of lipid membranes by photodynamic action via formation of hydrophobic defects or pre-pores.

To gain insight into mechanisms of photodynamic modification of biological membranes, we studied an impact of visible light in combination with a photosensitizer on translocation of various substances across artificial (vesicular and planar) bilayer lipid membranes (BLMs). Along with induction of carboxyfluorescein leakage from liposomes, pronounced stimulation of lipid flip-flop between the two monolayers was found after photosensitization, both processes being prevented by the singlet oxygen quencher sodium azide. On the contrary, no enhancement of potassium chloride efflux from liposomes was detected by conductometry under these conditions.

Light-triggered liposomal release: membrane permeabilization by photodynamic action.

Photosensitized damage to liposome membranes was studied by using different dye-leakage assays based on fluorescence dequenching of a series of dyes upon their release from liposomes. Irradiation of liposomes with red light in the presence of a photosensitizer, trisulfonated aluminum phthalocyanine (AlPcS(3)), resulted in the pronounced leakage of carboxyfluorescein, but rather weak leakage of sulforhodamine B and almost negligible leakage of calcein from the corresponding dye-loaded liposomes. The same series of selectivity of liposome leakage was obtained with chlorin e6 that appeared to be more potent than AlPcS(3) in bringing about the photosensitized liposome leakage.

Photodynamic activity and binding of sulfonated metallophthalocyanines to phospholipid membranes: contribution of metal-phosphate coordination.

Photosensitized efficacy of tetrasulfonated phthalocyanines of zinc, aluminum and nickel (ZnPcS(4), AlPcS(4) and NiPcS(4), respectively) as studied by gramicidin channel (gA) photoinactivation was compared with adsorption of the dyes on the surface of a bilayer lipid membrane as measured by the inner field compensation method. The adsorption of the negatively charged phthalocyanines on diphytanoylphosphatidylcholine (DPhPC) membranes led to formation of a negative boundary potential difference between the membrane/water interfaces. Good correlation was shown between the photodynamic activity and the membrane binding of the three metallophthalocyanines.

Production of reactive oxygen species in mitochondria of HeLa cells under oxidative stress.

Mitochondria can be a source of reactive oxygen species (ROS) and a target of oxidative damage during oxidative stress. In this connection, the effect of photodynamic treatment (PDT) with Mitotracker Red (MR) as a mitochondria-targeted photosensitizer has been studied in HeLa cells. It is shown that MR produces both singlet oxygen and superoxide anion upon photoactivation and causes photoinactivation of gramicidin channels in a model system (planar lipid bilayer).

Redox-regulated ion channel activity of a cysteine-containing gramicidin A analogue.

According to recent data, gramicidin A analogues having positively charged amino acid sequences at the C-termini exhibit two types of channel activity in lipid membranes: classical cation-selective channels and large unselective pores. The induction of unselective pores was shown here to strongly depend on the redox state of the membrane-bathing solution, if the gramicidin analogue contained a cysteine residue in the sequence GSGPKKKRKVC attached to the C-terminus. In particular, the addition of H2O2 led to an increase in the transmembrane current and the loss of cationic selectivity on planar bilayer lipid membranes and an increase in the carboxyfluorescein leakage of liposomes.

Large unselective pore in lipid bilayer membrane formed by positively charged peptides containing a sequence of gramicidin A.

Ion-channel activity of a series of gramicidin A analogues carrying charged amino-acid sequences on the C-terminus of the peptide was studied on planar bilayer lipid membranes and liposomes. It was found that the analogue with the positively charged sequence GSGRRRRSQS forms classical cationic pores at low concentrations and large unselective pores at high concentrations. The peptide was predominantly in the right-handed beta(6.