Regulation of JH titers: The relevance of degradative enzymes and binding proteins

Juvenile hormones play a crucial role in development, metamorphosis, and reproduction of insects. This mini-review discusses the nature of the juvenile hormones identified in insects and their changes in concentration in the hemolymph during development and reproduction. The hemolymph titer is largely determined by the rate at which juvenile hormones are synthesized and released by the corpora allata, but other factors are also involved in titer regulation, such as the affinity and concentration of juvenile hormone binding proteins in the hemolymph and the rate of juvenile hormone degradation in hemolymph and tissues. Juvenile hormone specific esterases occur in hemolymph and tissues, whereas epoxide hydrolases, which may degrade the hormone, are exclusively tissue bound. The activities of these degradative enzymes and the concentration of binding proteins change during the insect life cycle and these changes are related to fluctuations in hormone titer. However, we are still a long way from understanding the subtle interactions between these components in regulation of juvenile hormone titers. In particular, our knowledge is hampered by lack of information about the types, concentrations, and affinities of intracellular juvenile hormone receptors. © 1996 Wiley-Liss, Inc.