INCORPORATION OF PORIN IN BLACK LIPID MEMBRANES OF DIFFERENT COMPOSITION

The kinetic of pore formation induced by the porin of the outer membrane of ox brain mitochondria was studied by its incorporation in the black lipid membranes (BLM) made either of phosphatidylinositol (PI) or of oxidized cholesterol (OxChol). Porin incorporation was studied by means of alternate current (f=1Hz), recording the voltage after a current to voltage converter in series with the membrane. The addition of the porin to the bathing solution separated by black membrane either formed of PI or OxChol resulted in an increase of the voltage through the membrane. With PI membranes the time course of the voltage at the measurement device was S-shaped irrespective whether the porin was added to the aqueous solution on one side of the membrane or to both phases, or when the porin was already present in aqueous solution before to the formation of the membrane. With OxChol membranes the kinetic pattern changes, in that it shows an hyperbolic shape regardless if the porin was present at higher concentration or after the blackening of the membrane or when the protein was present before membrane formation. At lower concentration of porin the kinetic of incorporation in the OxChol membranes follows the same pattern, except the initial lag time due, presumably, to the time of diffusion of the molecules in the bathing solution. An other aspect of the behaviour displayed by this kind of membranes is that much lower concentration is required to determine the same increase of the electrical conductance. Probably either the polar head or/and the surface potential at the interface of the lipid membrane play a key role in the kinetic of the porin reconstitution.