Characterization of a salivary gland-specific esterase in the vector mosquito, Aedes aegypti

Esterase enzymatic activity was investigated in salivary gland lysates of adult Aedes aegypti. Esterases in lysates made from female glands had higher specific activity than those in lysates from male glands towards beta-naphthyl acetate but showed no difference with alpha-naphthyl butyrate as a substrate. Female salivary gland lysates showed no difference in activity to alpha- and beta-forms of naphthyl acetate and no discernable activity towards alpha-naphthyl caprate. Both female and male salivary gland lysates exhibited phosphatase enzymatic activity but the specific activities were lower than those seen for the esterase enzymatic activity. Salivary gland esterase activity was inhibited completely by paraoxon, para-hydroxymercurobenzoate, tetraethylammonium iodide and moderately by diisopropylfluorophosphate. Eserine and phenylmethylsulfonylfluoride had no effect on enzyme activity. In a probing assay, adults of both sexes were shown to secrete esterase in saliva. Esterase activity was present in the saliva of females probing for either a sugar meal or a blood meal. Furthermore, esterase was secreted from female salivary glands in culture. Histochemical analysis of dissected salivary glands showed that the majority of the esterase enzymatic activity was in the distal-lateral lobes of the female tissues, although the proximal-lateral and medial lobes also had activity. Male salivary glands stained uniformly over all of the lobes. A salivary gland-specific esterase, designated SG-EST, appears to account for the majority of enzyme activity in the glands. SG-EST was partially purified by electroelution of an active protein from native polyacrylamide gels, and has an approximate molecular weight of 65,000 Da. In separate experiments, affinity chromatography independently identified a single 65,000 Da protein likely to be SG-EST. Native electrophoretic analysis of salivary glands revealed that, while most enzyme activity is due to SG-EST, there are two other esterases present. One of these minor moieties is present in adult tissues in addition to the salivary gland, and the other is present throughout development. Possible functions of the salivary gland esterase are discussed.