MECHANISTIC STUDIES OF THE DEGRADATION OF JUVENILE-HORMONE ESTERASE IN MANDUCA-SEXTA

The mechanisms of degradation of juvenile hormone esterase (JHE) were investigated in larvae of the tobacco hornworm, Manduca sexta. JHE is removed From the hemolymph by the pericardial cells by receptor-mediat ed endocytosis and is ultimately degraded in the lysosomes. Immunoprec ipitation experiments and native PAGE followed by Western blotting sho wed that JHE associates with a putative heat shock cognate protein (Hs p). Approximately 25% of the active JHE in the pericardial cell comple x is associated with the putative Hsp 1 h postinjection of affinity pu rified JHE. Electron microscope analysis revealed that the putative Hs p is located in the trans-Golgi network of pericardial cells, where it is hypothesized to be involved in sorting of proteins destined for th e lysosomes, from those destined for the cell membrane. Data acquired from immunoprecipitation and Western blotting experiments argue agains t the involvement of ubiquitin in the degradation of JHE. Injection of radiolabeled JHE into larvae of M. sexta followed by SDS-PAGE of peri cardial cell homogenates revealed covalent binding of an unidentified protein to JHE in the pericardial cell complex. (C) 1997 Wiley-Liss, I nc.