Porin incorporation and channel formation in bilayer membranes have been investigated under different incorporation conditions (Gallucci et al Biophys. J. 71 824-831, 1996; Micelli et al., Biophys J.,1998 submitted) We have identified a process of positive/negative cooperativity which can be described by simple mathematical model depending. among others, on two growth rate parameters: K1 describing the insertion or positive cooperativity and K2 describing the negative cooperativity. This model takes into account for the kinetics growth and steady state phase of the insertion, using appropriate data acquisition (dependence of steady state conductance on porin concentration) and analytical techniques, we have provided indirect evidence that the porin channel shows well-defined properties of assambly into the bilayers. In this note we pursue our study in order to answer the following question: are the above-mentioned characteristics dependent on the surface charge ie membrane potential) of the bilayers? For this reason, using alternating current, we investigate the kinetics of porin incorporation into black lipid membranes (BLM) as a function of ionic strength, the BLM were made up of phosphatidylinositol (PI), oxidized cholesterol (Ox Ch). Our results indicate that bilayers with higher negative charge density are associated with a slower insertion rate K, and an almost constant negative cooperativity rate K₁. These results are corroborated, especially at lower ionic strength, by experiments in which Ba++ is added to the solution as a screening agent. Indeed, the K, parameter for Ox Ch, a neutral bilayer, is higher than that of the PI charged bilayer, and adding Ba++ to Ox Ch does not seem to affect either K1 or K2. Finally, the assembly properties of porin, as evaluated by fitting the data regarding the dependence of steady state conductance Gmss on porin concentration for three different ionic strength (0.1, 0.5 and 1 M), seem to be dependent on the ionic strength and membrane substrate
Porin incorporation in BLM controlled by surface potencial
MELELEO D.;
1999-01-01
Abstract
Porin incorporation and channel formation in bilayer membranes have been investigated under different incorporation conditions (Gallucci et al Biophys. J. 71 824-831, 1996; Micelli et al., Biophys J.,1998 submitted) We have identified a process of positive/negative cooperativity which can be described by simple mathematical model depending. among others, on two growth rate parameters: K1 describing the insertion or positive cooperativity and K2 describing the negative cooperativity. This model takes into account for the kinetics growth and steady state phase of the insertion, using appropriate data acquisition (dependence of steady state conductance on porin concentration) and analytical techniques, we have provided indirect evidence that the porin channel shows well-defined properties of assambly into the bilayers. In this note we pursue our study in order to answer the following question: are the above-mentioned characteristics dependent on the surface charge ie membrane potential) of the bilayers? For this reason, using alternating current, we investigate the kinetics of porin incorporation into black lipid membranes (BLM) as a function of ionic strength, the BLM were made up of phosphatidylinositol (PI), oxidized cholesterol (Ox Ch). Our results indicate that bilayers with higher negative charge density are associated with a slower insertion rate K, and an almost constant negative cooperativity rate K₁. These results are corroborated, especially at lower ionic strength, by experiments in which Ba++ is added to the solution as a screening agent. Indeed, the K, parameter for Ox Ch, a neutral bilayer, is higher than that of the PI charged bilayer, and adding Ba++ to Ox Ch does not seem to affect either K1 or K2. Finally, the assembly properties of porin, as evaluated by fitting the data regarding the dependence of steady state conductance Gmss on porin concentration for three different ionic strength (0.1, 0.5 and 1 M), seem to be dependent on the ionic strength and membrane substrateI documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
