Antibacterial hemolymph proteins of Manduca sexta

Exclusion column fractionated immune hemolymph of the M. sexta larva contains five peaks of anti-E. coli activity with molecular weights of greater than 140 kD and approximately 91, 54, 14 and 4 kD, plus one peak of lysozyme activity with a molecular weight of 17 kD. Purification of the 54 kD peak showed that this peak consists of the previously described M18 proteins which have monomeric weights of approximately 20 kD and had antibacterial activity against certain gram negative bacteria. Approximately 80% of the total hemolymph antibacterial activity was detected in the 14 and 4 kD peaks. These proteins, which kill both gram negative and gram positive bacteria, appeared to be directly analogous to the cecropins of H. cecropia. The greater than 140 and 91 kD peaks constituted only a minor part of the total antibacterial activity.