BIOCHEMICAL-CHARACTERIZATION OF JUVENILE-HORMONE ESTERASES FROM LINESSELECTED FOR HIGH OR LOW ENZYME-ACTIVITY IN GRYLLUS-ASSIMILIS

In a previous study, activity of the insect endocrine regulator juveni le hormone esterase (JHE), in the cricket Gryllus assimilis, was subje cted to bidirectional selection. This resulted in three pairs of high- and low-selected lines, each of which differed by 3.5-fold in JHE act ivity. In the present study, juvenile hormone esterases from these lin es were characterized with respect to the Michaelis constant (K-m), th ermostability, and inhibition. None of three high-selected JHEs differ ed from its respective low-selected JHE in the Michaelis constant (K-m ) for juvenile hormone. Similarly, the high-selected JHEs did not diff er from tile low selected JHEs in thermostability ol inhibition by eit her of two general esterase inhibitors (DFP, eserine) or a ''JHE-speci fic'' inhibitor (OTFP). Thus no evidence was obtained to suggest that the response to selection was due to allozymes or isozymes with altere d kinetic or stability properties. Kinetic and stability properties we re also very similar for the JHEs from the three high- selected or the three low-selected lines. Finally, none of the thermostability or inh ibition profiles for any of the six JHEs exhibited sharp discontinuiti es thus providing Mo evidence for the existence of multiple isozymes. The available evidence points to genetically variable regulators which affect the synthesis degradation, or tissue distribution of JHE as be ing responsible for the divergence in JHE activity between the selecte d lines.