Biochemical and immunological properties of different electrophoretic forms of juvenile hormone esterase from Trichoplusia ni (Hübner)

Abstract

The two major electrophoretic forms (p I 5.5, 5.3) of juvenile hormone esterase were independently isolated from hemolymph of larval Trichoplusia ni. A simple and rapid preparation procedure of poly(ethylene glycol) precipitation, Sephadex gel filtration and chromatofocusing is described. Analytical isoelectric focusing showed only one peak of juvenile hormone esterase activity in the respective purified samples, whereas there were four (two major) such peaks in the hemolymph. The amino acid composition of the two forms was similar. The comparison of peptides obtained after protein fragmentation bycyanogen bromide showed that juvenile hormone esterases A and B were very similar, although definitely not identical, in amino acid sequence. The immunological comparisons of juvenile hormone esterases suggested that the number of polyclonal antibody binding sites on both forms was the same. There were no detected differences between immunoreactive properties of juvenile hormone esterase from the hemolymph of different stages of larval maturation. The influence of the active site of the enzyme on its antigenic properties was studied by immunocompetition. The inactive, heat-denatured juvenile hormone esterase can only partially protect against inhibition of its activity by the antibodies, whereas an organophosphate inhibitor which covalently binds to the catalytic center of the enzyme did not change the immunoreactive properties in comparison to active juvenile hormone esterase from hemolymph. These data show that heat-denatured juvenile hormone esterase has lost at least one or more epitopes, but the catalytic site of the enzyme is distinct from the epitopes.