Lytic activity of monomeric and oligomeric melittin

The haemolytic activities of melittin and melittin tetramer as induced by high phosphate counterion concentration, were monitored. Monomeric melittin was found to be fully lytic, whilst tetrameric melittin lacked such activity. Under conditions where melittin was fully tetrameric attempts were made to covalently cross-link the native tetramer using a series of different chain length bifunctional imido esters. The cross-linked oligomers were fully lytic under conditions where melittin was demonstrated to lack such activity. This finding, together with molecular weight determinations and circular dichroism studies, indicated that the cross-linked melittin was quite different to the native tetramer. The haemolytic activity of melittin-containing solutions was related to the concentration of monomeric melittin. The effect of reduced dielectric constant (epsilon) on the aggregation behaviour of melittin and its derivatives was found to favour monomeric melittin.