THE ROLE OF STEROLS IN THE FUNCTIONAL RECONSTITUTION OF WATER-SOLUBLEMITOCHONDRIAL PORINS FROM PLANTS

Water-soluble porins were prepared from native mitochondrial porins is olated from different plants (pea and corn). In the water-soluble form the porins have lost their channel-forming properties. The water-solu ble porins were investigated for the influence of different sterols on their membrane activity and their channel-forming properties in lipid bilayer membranes. Our experiments demonstrated that the water-solubl e porins regained channel forming activity when the protein was preinc ubated with different sterols in the presence of a detergent. The chan nels formed in lipid bilayer membranes after this procedure regain in many but not all cases the original properties of the native mitochond rial porins. Preincubation with other sterols led to a change in the s ingle-channel conductance or to a complete loss of the voltage depende nce. The sterols had also a strong influence on the channel-forming ac tivity of the porins. Preincubation of water-soluble pea porin with th e plant sterol p-sitosterol resulted in a considerable higher channel- forming activity than with all the other sterols used for preincubatio n. The role of the sterols in the channel-forming complex is discussed .