Biochemical characterization of juvenile hormone esterases from lines selected for high or low enzyme activity inGryllus assimilis

Abstract

In a previous study, activity of the insect endocrine regulator juvenile hormone esterase (JHE), in the cricketGryllus assimilis, was subjected to bidirectional selection. This resulted in three pairs of high- and low-selected lines, each of which differed by 3.5-fold in JHE activity. In the present study, juvenile hormone esterases from these lines were characterized with respect to the Michaelis constant (K _m), thermostability, and inhibition. None of three high-selected JHEs differed from its respective low-selected JHE in the Michaelis constant (K _m) for juvenile hormone. Similarly, the high-selected JHEs did not differ from the low selected JHEs in thermostability or inhibition by either of two general esterase inhibitors (DFP, eserine) or a “JHE-specific” inhibitor (OTFP). Thus no evidence was obtained to suggest that the response to selection was due to allozymes or isozymes with altered kinetic or stability properties. Kinetic and stability properties were also very similar for the JHEs from the three high-selected or the three low-selected lines. Finally, none of the thermostability or inhibition profiles for any of the six JHEs exhibited sharp discontinuities, thus providing no 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 being responsible for the divergence in JHE activity between the selected lines.