Effect of sucrose feeding on the induction of honeybee haemolymph glucosidase (E.C. 3.2.1.20)

The kinetic properties (i.e maximum velocity V_m, dissociation constant K_h, and Hill coefficient h) of the ex-glucosidase complex of honeybee haemolymph have been studied in adult workers, from emergence to day 16, under continuous feeding with 2-M sucrose, alone or with the addition of 1.6-mM chloramphenicol as an inhibitor of protein synthesis (IPS). In the absence of IPS, V_m gradually increases to reach 40 times the initial value by day 16, with a trough of 8-12 times the initial value at days 9-12. In the presence of IPS, V_m values are consistently depressed by a factor increasing from 1.2 at day 2 to 3.6 at day 16. The constant K_h, is essentially unaffected both by time and by IPS treatment, while the Hill coefficient remains close to 1 or slightly lower with minor exceptions. These data suggest a true induction mechanism via the synthesis of new enzyme molecules, together with the possibility of modifications in the mode of aggregation of enzyme protomers.