FG Nanobiotechnologie
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An effect of the lipid hydrolysis products on the phospholipase A₂ action towards lipid monolayer
(1994)
The effect of lauric acid (LA) and lysolauroyllecithin (LLL) on the hydrolysis of lipid in monolayer by phospholipase A₂ from Bee venom was studied. It was found that LLL inhibits phospholipase action under both high (39 mN/m) and low (25 mN/m) surface pressure. On the other hand, LA inhibits phospholipase action under the low surface pressure (15 mN/m or 25 mN/m), but increases enzyme activity under high surface pressure (39 mN/m). This activating effect can be suppressed by high ionic strength of the aqueous subphase. It is suggested that an increase of the negative surface charge of the lipid monolayer, followed by an increase of the local concentrations of the positively charged enzyme and calcium near the monolayer is a coupling factor between fatty acid accumulation and phospholipase activation. Such an autocatalytic process can only occur when the substrate is organised into monolayer, bilayer or micelles, therefore it can be considered as a reason for the substrate activation and induction time before lipid hydrolysis.
An effect of the phospholipase A2 on the electrical potential distribution through lipid bilayer
(1992)
Photosensitized damage of bilayer lipid membrane in the presence of hematoporphyrin dimethylether
(1991)
The variations in electrical conductivity and surface tension of planar bilayer lipid membranes (BLMs) sensitized by a haematoporphyrin dimethylether (HpDME) on visible light irradiation are reported. The irradiation of BLMs immediately leads to a decrease in membrane surface tension. On irradiation the conductivity of BLMs remains constant for a certain period of time (induction time), followed by an increase, terminated by membrane breakage. The induction time is not dependent on stirring of the solution, the addition of azide or ferricyanide to the solution, the addition of antioxidant to the lipid or substitution of air for argon in the cell. The induction time decreases for repeated irradiations or for any new BLM formed in the same cell immediately after the previous membrane has been broken. The conductivity shift consists of reversible and irreversible components. These results suggest that the irradiation of BLMs sensitized by HpDME leads to an accumulation of photoproducts in the membrane which induce pore formation and to a decrease in BLM stability when the concentration of the photoproducts exceeds a critical level.
To evaluate phospholipase A activity a new assay is suggested. This assay is based on the recording of boundary potential changes of the planar bilayer lipid membrane during enzymatic hydrolysis of lipids. To register these changes, a second harmonic method is used. Sensitivity of the assay is about 0.0002 units/ml regardless of the impurities that may be present in the samples. One analysis takes about 5 min.
Current-voltage dependences for different tentative bacteriorhodopsin models were studied in order to explain the linearity of this dependence observed in our previous experiments. It is proved that the best correspondence with experiment occurs when the passive proton transport path is assumed to contain many binding sites and the thickness of the widest barrier separating these sites is not more than 1 nm. One of the following two conditions is necessary: (1) electrostatic repulsion of protons in the channel is so strong that not more than one proton can be in the channel at a time; the potential energy of a proton in this channel decreases linearly towards the active site. (2) Electrostatic repulsion between protons in the channel is moderate, and the binding energy of a proton at all channel sites is equal. Under conditions of high channel occupation, single-file effects lead to non-linearity of the current-voltage characteristics if there is no electrostatic repulsion.