The rate of fusion of phospholipid vesicles and the role of bilayer curvature.
Explore the source record for details and available documents.
Kinetics↗
Biomedical subjects
J Bentz
Publications and source records attributed to J Bentz.
Interactions of La2+ with phosphatidylserine vesicles: binding, phase transition, leakage, 31P-NMR and fusion.
The interaction of La2+ with phosphatidylserine vesicles is studied by differential scanning calorimetry, 140La binding, 31P-NMR chemical shifts and relaxation rates, carboxyfluorescein and [14C]sucrose release, X-ray diffraction and freeze-fracture electron microscopy. In the presence of La3+ concentrations above 1 mM and an incubation temperature of 38 degrees C, i.e., at the phase transition temperature of the complex La/phosphatidylserine, the binding ratio of La/lipid exceeds a 1/3 ratio, reaching saturation at a 1/2 ratio. Analysis, employing a modified Gouy-Chapman equation, indicates a significant increase in the intrinsic binding constant of La/phosphatidylserine when the La3+ concentrations exceeds the threshold concentration for leakage. The analysis illustrates that at the molecular level the binding of La3+ can be comparable to or even weaker than that of Ca2+, but that even when present at smaller concentrations La3+ competes with and partially displaces Ca2+ from membranes or other negatively charged surfaces. The results suggest that the sequence La3+ greater than Ca2+ greater than Mg2+ reflects both the binding strength of these cations to phosphatidylserine as well as their ability to induce leakage, enhancement of 31P spin-lattice relaxation rates, fusion and other structural changes. The leakage, fusion, and other structural changes are more pronounced at the phase transition temperature of the La/lipid complex.
Electron Spin Resonance Spectroscopy↗
Calcium- and magnesium-induced fusion of mixed phosphatidylserine/phosphatidylcholine vesicles: effect of ion binding.
The aggregation, leakage, and fusion of pure PS (phosphatidylserine) and mixed PS/PC (phosphatidylcholine) sonicated vesicles were studied by light scattering, the release of encapsulated carboxyfluorescein, and a new fusion assay which monitors the mixing of the internal compartments of fusing vesicles. On a time scale of 1 min the extent of fusion was considerably greater than leakage. The Ca2+ and Mg2+ concentrations required to induce fusion increased when the PS content of the vesicles was decreased, and/or when the NaCl concentration was increased. Calculations employing a modified Gouy-Chapman equation and experimentally determined intrinsic binding constants of Na+ and Ca2+ to PS were shown to predict correctly the amount of Ca2+ bound in mixed PS/PC vesicles. For vesicles composed of either pure PS or of mixtures with PC in 100 mM NaCl (4:1 and 2:1 PS/PC); the induction of fusion (on a time scale of minutes) occurred when the amount of Ca or Mg bound/PS molecule exceeded 0.35-0.39. The induction of fusion for both pure PS and PS/PC mixed vesicles (with PS exceeding 50%) can be explained by assuming that destabilization of these vesicles requires a critical binding ratio of divalent cations to PS.
Binding Sites↗
Aggregation of colloidal particles modeled as a dynamical process.
Aggregation kinetics of sonicated phosphatidylserine (PtdSer) vesicles in NaCl indicate that the process is fully reversible and dynamical, involving the rapid formation and dispersal of aggregates. Accordingly, the general mass action kinetic equations are analyzed with respect to the equilibrium state and the formation of higher order aggregates. For a general class of systems, the values for the mass average aggregate size at equilibrium are obtained from simple closed-form expressions. It is shown that an analysis of the aggregation equilibrium will yield estimates for the potential energy well that holds the aggregates together. A fit to the experimental data for kinetics of Na+-induced aggregation of the vesicles has been achieved by employing mass action kinetic equations that include the dissociation reactions. The threshold of NaCl concentration required for aggregation involves the clear distinction between the rate and extent of aggregation.
Colloids↗
Mass action kinetics of phosphatidylserine vesicle fusion as monitored by coalescence of internal vesicle volumes.
The kinetics of Ca2+-induced fusion of sonicated phosphatidylserine vesicles is analyzed by means of the mass action model. The results of calculations are shown to simulate the experimental results for the mixing of aqueous vesicle volumes, release of vesicle contents and for the observed increase in light scattering [Wilschut, J., Düzgünes, N., Fraley, R., & Papahadjopoulos, D. (1980) Biochemistry (first of three papers in this issue)]. The calculations give the distribution of vesicle sizes during the initial stages of the fusion process and an estimate for the occurrence of multiple fusion events. It is estimated that during the first few seconds from the beginning of the fusion process in the above systems only a small fraction of the material trapped will leak during each fusion event. The fraction of material which leaks per fusion event is further reduced with increased Ca2+ concentrations. The values of the rates of fusion which describe the above experiments suggest that the rate limiting step of the overall fusion reaction is the aggregation and close approach of vesicles to each other rather than the fusion event per se.
Calcium↗
Cation binding to membranes: competition between mono-, di- and trivalent cations.
Explore the source record for details and available documents.
Cations↗
Reversibility of sodium-induced aggregation of sonicated phosphatidylserine vesicles.
The kinetics of sodium-induced aggregation of sonicated phosphatidylserine vesicles has been studied as a function of sodium concentration and temperature. The concentration threshold for aggregation induced by monovalent sodium has been found to be 550 mM sodium by stopped-flow rapid-mixing techniques. This aggregation is completely reversible to changes in sodium ion concentration and to changes in temperature. The aggregation rate decreases with increasing temperature, indicating that the backward reaction rate increases more rapidly with temperature than does the forward rate.
Cell Aggregation↗