Magainin 2 amide and analogues. Antimicrobial activity, membrane depolarization and susceptibility to proteolysis

We compared the abilities of synthetic magainin 2 amide and its analogues to inhibit the growth of Escherichia coli and to cause membrane depolarization in E. coli cells and cytochrome oxidase liposomes. The analogue, magainin A, was about 40-times more active than magainin 2 amide in inhibiting the growth of E. coli and had a much more sustained effect on the membrane potential. In the liposomal system, however, there was only approx. 20% difference between these two peptides in the reduction of membrane potential and uncoupling of respiration. Studies with pronase digestion suggested that the difference in potency may be due to differential susceptibility to proteolysis in the presence of membranes.