REGULATION OF JH TITERS - THE RELEVANCE OF DEGRADATIVE ENZYMES AND BINDING-PROTEINS

Juvenile hormones play a crucial role in development, metamorphosis, a nd reproduction of insects. This mini-review discusses the nature of t he juvenile hormones identified in insects and their changes in concen tration in the hemolymph during development and reproduction. The hemo lymph titer is largely determined by the rate at which juvenile hormon es are synthesized and released by the corpora allata, but other facto rs are also involved in titer regulation, such as the affinity and con centration of juvenile hormone binding proteins in the hemolymph and t he rate of juvenile hormone degradation in hemolymph and tissues. Juve nile hormone specific esterases occur in hemolymph and tissues, wherea s epoxide hydrolases, which may degrade the hormone, are exclusively t issue bound. The activities of these degradative enzymes and the conce ntration of binding proteins change during the insect life cycle and t hese changes are related to fluctuations In hormone titer. However, we are still a long way from understanding the subtle interactions betwe en these components in regulation of juvenile hormone titers. In parti cular, our knowledge is hampered by lack of information about the type s, concentrations,and affinities of intracellular juvenile hormone rec eptors. (C) 1996 Wiley-iiss, Inc.