The interaction of hematoporphyrin IX (HP) with artificial bilayer lipid membranes (BLMs) has been studied. It has been found that after dark incubation of BLMs in a HP solution (at concentrations from $10^{-6}$ to $3 \cdot 10^{-5}$ M) the conductance of the BLMs does not change very much, the elasticity modulus ( $E_{\perp}$ ) and the dynamic viscosity coefficient $\eta$ diminish by 21.9-31.3%, while the membrane potential $U_1$ becomes negative (-50 mV). Irradiation of a modified BLM by a He-Ne laser leads to an increase of the parameters $E_{\perp}$ aud $\eta$ by 40.7 to 66.2%, to a decrease of $U_1$ to -20 mV, and also to irreversible changes in the mechanical properties of the membrane. Binding of HP with BLM proceeds noncooperatively with the constant $К = 10^{5}$ $М^{-1}$.
$^1$Faculty of Mathematics and Physics, Komenius University, Bratislava. Czechoslovakia
$^2$Department of General Physics and Wave Processes, Faculty of Physics, Moscow State University, Leninskie Gory, Moscow, 119992, Russia