TIME-INTERVAL MEASURING ENZYME FOR RESUMPTION OF EMBRYONIC-DEVELOPMENT IN THE SILKWORM, BOMBYX-MORI

Time measurement by esterase A4 (Ease A4) purified from Bombyx diapausing eggs has been studied using ATP as a substrate. At 5 degrees C, the ATPase activity of Ease A4 was very low initially, but in 2 weeks activity increased sharply and then rapidly fell, The period required to activate the enzyme was equivalent to that observed in vivo and was coincident with the chilling period indispensable for diapause termination. Ease A4 extracted from the eggs that had been chilled for 10 days reached a peak in a few days which implies that activation took place 2 weeks after chilling even if the chilling resulted from a combination of 10 days in vivo and a few days in vitro, The duration of chilling was the critical factor in its activation. The re-inactivated enzyme could be regenerated by guanidine-HCl (GuHCl) treatment, The GuHCl effect was also observed during the initial activation of the enzyme. GuHCl reset the Ease A4 so that another 2 weeks was needed for activation. It is concluded that the Ease A4 may undergo conformational changes by an identical mechanism both in vivo and in vitro, resulting in a time-interval activation of the enzyme which is crucial for diapause termination by cold.