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

Time measurement by esterase A4 (Ease A4) purified from Bombyx diapaus ing eggs has been studied using ATP as a substrate. At 5 degrees C, th e ATPase activity of Ease A4 was very low initially, but in 2 weeks ac tivity increased sharply and then rapidly fell, The period required to activate the enzyme was equivalent to that observed in vivo and was c oincident with the chilling period indispensable for diapause terminat ion. 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 combinati on of 10 days in vivo and a few days in vitro, The duration of chillin g was the critical factor in its activation. The re-inactivated enzyme could be regenerated by guanidine-HCl (GuHCl) treatment, The GuHCl ef fect was also observed during the initial activation of the enzyme. Gu HCl reset the Ease A4 so that another 2 weeks was needed for activatio n. It is concluded that the Ease A4 may undergo conformational changes by an identical mechanism both in vivo and in vitro, resulting in a t ime-interval activation of the enzyme which is crucial for diapause te rmination by cold.