HEMATOPORPHYRIN DIMETHYL ETHER TRANSPORT ACROSS BILAYER-LIPID MEMBRANE

Changes of the transmembrane potential across planar bilayer lipid mem brane (BLM) in the presence of a protonophore were observed upon addit ion on haematoporphyrin dimethyl ether (HPDME) at one side of BLM. The sign of the potential corresponded to the pH reduction at the same si de. The subsequent illumination of the cell was followed by the transm embrane potential changing in the opposite direction reaching a statio nary value. The potential increased up to the previous level in the da rk. By the method of compensation of intramembrane field, changes in t he boundary potentials were found, providing the evidence for the adso rption of HPDME anions. These changes increased with the decrease of b uffer capacity of solution or under transmembrane gradient of pH. As f ar as the presence of HPDME did not influence either the conductivity of BLM or pH value in the bulk of solution, the results obtained were interpreted within the frame of the following model. The HPDME molecul es are adsorbed on the membrane surface as anions, and transported acr oss the membrane in neutral Term after the protonation of one of the H PDME forms so that pH changes only in the unstirred layers.