Proteolytic Enzymes from Larvae of the Fire Ant, Solenopsis invicta

Abstract

The imported red fire ant (Solenopsis invicta) is a problematic pest in the Southern United States. The stages of development for these ants are as follows: egg, 1st, 2nd, 3rd, and 4th instar larvae, prepupae, pupae, and adult. The 4th instar larvae plays an important role in the survival of the colony in that it is totally responsible for the digestion of solid foods and the source of nutrients for the queen and adult workers. In our studies we have been successful in purifying and characterizing four proteinases from the 4th instar larvae. Based on substrate specificity, they appear to represent two chymotrypsin-like and two elastase-like proteinases. These are referred to as Soli C1, Soli C2, Soli E1, and Soli E2, with molecular masses of 25, 28, 23, and 24 kDa, respectively, based on SDS-PAGE. All enzymes were inhibited by diisopropyl fluorophosphate, a general serine class inhibitor. Various synthetic substrates with either Phe or Val in the P-1 position, were readily cleaved by Soli C1/C2 or E1/E2, respectively. Each enzyme has been characterized as to pH optimum, pH stability, isoelectrofocusing and susceptibility to inhibition by a broad range of natural and synthetic proteinase inhibitors. Such compounds may prove useful for the development of insecticides to control fire ant infestation.