SURFACE-ACTIVITY PROPERTIES OF CYSTEINE-SUBSTITUTED C-TERMINAL MELITTIN ANALOGS

In order to extend our knowledge of factors important in the surface a ctivity of melittin, cysteine was substituted for lysine-21 and lysine -21/glutamine-25 in a pair of synthetic peptide analogues. The first o f these changes resulted in only modest effects on secondary structure (determined in 50% trifluoroethanol), emulsification and surface tens ion properties. Introduction of a second cysteine greatly reduced both the rate of surface tension decay and the equilibrium surface tension attained. although secondary structure (determined in 50% trifluoroet hanol) was only slightly affected by this modification. This latter pe ptide completely lacked emulsification and haemolytic proper ties and was found to oligomerise readily due to the formation of intermolecula r, disulphide bridges. These results indicate that oligomerisation abo lishes surface activity in melittin.