Import of a mitochondrial presequence into protein-free phospholipid vesicles

A synthetic mitochondrial presequence has been shown to translocate across pure phospholipid bilayers. The presequence was fluorescently labeled so that its association with membranes could be monitored spectroscopically. In the presence of large unilamellar vesicles, the presequence showed time- and potential-dependent protection from reaction with added trypsin and dithionite. The protection was rapidly reversed by treatment of the vesicles with detergent. If the vesicles contained trypsin, the added presequence became sensitive to digestion by the protease. The results show that a mitochondrial presequence can translocate across phospholipid bilayers that lack a hydrophilic translocation pore.