Adsorption of polyvalent cations to bilayer membranes from negatively charged lipid: estimating the lipid accessibility in the case of complete binding.
The effect of trivalent (Gd(3+) and Yb(3+)) and divalent (Be(2+) and Ca(2+)) cations on suspensions of multilamellar liposomes formed from brain PS and DMPS has been studied using microelectrophoresis and DSC techniques, respectively. The zeta potential values have been shown to strongly depend on the total lipid concentration in the suspension. At moderate concentrations of the polyvalent cations, the total cation concentration exceeds the bulk one several times due to adsorption of cations to the liposomes. A modification of the Gouy-Chapman-Stern theory in the case of unknown bulk concentration of the polyvalent cation is presented. An intrinsic association constant for Be(2+) ions was evaluated to be about K(2) approximately 50 M(-1). The algorithm for estimating the concentrations of the accessible (to exogenously added polyvalent cations) lipid-binding sites is described. These values are consistent with the subsurface concentrations of the polyvalent cations, which monotonously increase with the total concentration of the polyvalent cations. The calculated lipid accessibilities are shown to be in accordance with the DSC data.
Averbakh
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A
Institute of Chemical Physics, Chernogolovka, Region, Moscow, Russia.
Lobyshev
V I
VI
D000327:Adsorption; D000818:Animals; D001608:Beryllium / Q000378:metabolism; D001921:Brain / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002152:Calorimetry, Differential Scanning; D002412:Cations / Q000378:metabolism*; D004586:Electrophoresis; D005682:Gadolinium / Q000378:metabolism; D008051:Lipid Bilayers / Q000378:metabolism*; D008081:Liposomes / Q000378:metabolism; D008566:Membranes / Q000378:metabolism; D008956:Models, Chemical; D015233:Models, Statistical; D013696:Temperature; D015018:Ytterbium / Q000378:metabolism
D002412:Cations; D008051:Lipid Bilayers; D008081:Liposomes; D005682:Gadolinium; D015018:Ytterbium; D001608:Beryllium; D002118:Calcium