ANTIBACTERIAL PEPTIDES AND MITOCHONDRIAL PRESEQUENCES AFFECT MITOCHONDRIAL COUPLING, RESPIRATION AND PROTEIN IMPORT

Cecropins A and P1, antibacterial peptides from insects and from pig a nd some related peptides released respiratory control, inhibited prote in import and at higher concentrations also inhibited respiration. How ever, PR-39, an antibacterial peptide from pig intestine, was found to be almost inert towards mitochondria. The concentrations at which the three mitochondrial functions were effected varied for different pept ides. Melittin, magainin and Cecropin-A-(1,13)-Melittin(1,13)-NH2, a h ybrid between cecropin A and melittin, were most potent, while the two cecropins acted at higher concentrations. The biosynthesis of cecropi n A is known and the intermediates are synthesized. We have used four peptides from this pathway to investigate their effects on coupling, r espiration and protein import into mitochondria. Mature cecropin A fol lowed by the preproprotein were most aggressive whereas the intermedia tes were less active or inert. The efficiency of different derivatives of cecropin A as uncouplers correlates well with their capacity to re lease membrane potential measured as fluorescence quenching of Rhodami ne 123. Inhibition of respiration was found to be dependent on membran e potential and was most pronounced with mature cecropin A, less so wi th its three precursors. We also found that three peptides derived fro m mitochondrial presequences showed antibacterial activity. It is conc luded that, there are similarities in the functions of antibacterial p eptides and mitochondrial presequences, uncoupling activity in mitocho ndria cannot be correlated with the antibacterial activity (contrary t o a previous suggestion), the processing of preprocecropin A may have evolved in such a way that there is a minimum of membrane damage from the intermediates in the pathway, and peptides produced for delivery o utside of an animal have evolved to be more aggressive against mitocho ndria than peptides for delivery inside of the animal.