Abstract
The mode of action of a bactericidal protein (sarcotoxin I) purified from the haemolymph of Sarcophaga peregrina (flesh-fly) larvae was studied, focusing attention on its effect on the function of the membrane of Escherichia coli. Sarcotoxin I almost completely blocked the uptakes of tetraphenylphosphonium ion and proline, which are known to be driven by a membrane potential, indicating that this protein disrupts the membrane potential of bacteria.