Juvenile hormone esterases of Lepidoptera II. Isoelectric points and binding affinities of hemolymph juvenile hormone esterase and binding protein activities

The juvenile hormone esterase (JHE) and juvenile hormone binding protein (JHBP) activities from the last larval instar of 14 species of Lepidoptera (Pieris rapae, Colias eurytheme, Danaus plexippus, Junonia coenia, Hemileuca nevadensis, Pectinophora gossypiella, Spodoptera exigua, Trichoplusia ni, Heliothis virescens, Orygia vetusta, Ephestia elutella, Galleria mellonella, Manduca sexta and Estigmene acrea) were analyzed by analytical isoelectric focusing (IEF). While the multiplicity and isoelectric point of these proteins varied, all of them were mildly acidic (pI 4.0-7.0), and a large number of the species possessed only a single JHE and/or JHBP activity. The Michaelis constants (K_m's) of the whole hemolymph JHE activities from selected species for JH III were in the range of 10^-7M. The equilibrium dissociation constant K_d of the JHBP was determined by Scatchard analysis for selected species as well, with the majority of species having a K_d near 10^-7M. This information is consistent with JHE acting as a scavenger for JH at various times during development and relying entirely on mass action to remove JH from its protective JHBP complexes. The JHBP should limit nonspecific binding and thus facilitate the rapid transport of the intact hormone through-out the hemocoel. These data indicate that the species currently used in the study of the developmental biology of the Lepidoptera are biochemically similar to a variety of other species in this order.