[Mode of proteoliposome association with the planar bilayer phospholipid membrane]

Proteoliposomes were reconstituted from bacteriorhodopsin sheets, azolectin and cholesterol with or without nystatin. The bacteriorhodopsin-mediated electrogenesis was monitored using proteoliposome suspension and phenyldicarbaundecaborane (PCB-) probe or proteoliposomes associated with a planar bilayer membrane. In the light PCB- was shown to be absorbed by proteoliposomes. The PCB- uptake was inhibited by nystatin added to the incubation mixture containing proteoliposomes when the latter were reconstituted in the presence of nystatin. Extraproteoliposomal nystatin had no influence when nystatin was omitted from the reconstitution system. The nystatin-containing proteoliposomes were associated with a planar bilayer azolectin membrane in the presence of Ga2+. In such a system bacteriorhodopsin generates a photocurrent which charges the proteoliposome-containing (cis-side) compartment negatively and the trans-side compartment positively. The photoresponse was shown to be increased severalfold when nystatin was added to the trans-side solution. Nystatin addition was ineffective when proteoliposomes were reconstituted without nystatin. Taking into account the fact that nystatin forms ion-permeable pores in a membrane only when present on both sides of the membrane and when this membrane is a bilayer one, one can explain the above data assuming that (i) the intraproteoliposomal solution does not mix with the extraproteoliposomal one when the proteoliposomes are attached to a planar black membrane and (ii) the attached proteoliposomes are separated from the trans-side bathing solution with a bimolecular membrane. If this is the case, nystatin in the trans-side bathing solution and inside the attached proteoliposomes can form pores across the part of the planar membrane which separates the proteoliposome interior from the trans-side solution.(ABSTRACT TRUNCATED AT 250 WORDS)