Characterization of juvenile hormone esterase from genetically-determined wing morphs of the cricket, Gryllus rubens

Abstract

Long-winged (LW) vs short-winged (SW) genetic stocks of the cricket Gryllus rubens differ in plasma juvenile hormone esterase (JHE) activity during the last stadium. These activity differences may be important in morph determination. In the present study, plasma JHEs from the LW vs SW stocks were characterized with respect to a variety of kinetic and physical characteristics. Gel permeation chromatography of LW or SW plasma each resulted in a single JHE peak of high molecular weight (190 kDa). This molecular weight is about twice as high as that of JHEs from most other insects. The apparent Michaelis constant for JH III ranged from 47 to 81 nM. Like JHEs from other insects, the enzyme from G. rubens was inhibited strongly by trifluoropropanone transition-state analogs and weakly by the general esterase inhibitors, eserine and DFP. JHEs from LW and SW plasma exhibited no significant differences in K M, inhibition by trifluoropropanone or general esterase inhibitors, thermal denaturation profiles or pH profiles. The absence of K M differences between LW and SW JHEs indicate that the 2–4 fold higher enzyme activity in LW plasma, previous documented in assays employing saturating substrate concentration, will exist under physiological substrate concentrations. Two isoforms (pI = 5.1, 4.2−4.1) were identified in SW plasma but only the more acidic form was observed in LW plasma. This is the first documentation of genetically-determined differences in JHE isozymes in any insect species. However, the functional significance of these isoform differences, if any, remains to be established. These results provide no evidence that the plasma JHE activity differences between LW and SW stocks results from allozymes or isozymes with altered kinetic or stability characteristics.