Thermodynamics and kinetics of incorporation into a membrane.

Some very recent work on the equilibrium and rate of incorporation of the pore forming peptide alamethicin into phospholipid bilayers is briefly reviewed. The experimental methods and the proceedings to evaluate and interpret the data are generally applicable analogously to other cases of substrates which somehow associate with a membrane. For the special system under consideration, a very high degree of incorporation is observed, reflecting internal aggregation and thermodynamically non-ideal repulsive interactions. These points are included in a basic model which is shown to provide a quantitative fit of the measured results. Stopped-flow experiments have shown that the overall incorporation occurs as a practically one-step process. Its rate is remarkably fast, only slightly slower than the diffusion controlled upper limit. All the kinetic data can be quite satisfactorily interpreted in terms of a reaction scheme with steady-state intermediates comprising the obvious diffusional translocations as well as the accompanying conformational change. In particular, the special findings for the alamethicin system suggest a most simple working hypothesis of the molecular mechanism underlying the voltage-dependent gating effect.