INACTIVATION OF -ECDYSONE AND CYASTERONE BY LARVAE OF THE FLESHFLY, SARCOPHAGA PEREGRINA, AND PUPAE OF THE SILKWORM, SAMIA CYNTHIA

¹ The Biological Laboratories, Harvard University, Cambridge, Massachusetts 02138

1. The phytoecdysone, cyasterone, is twice as active as authentic -ecdysone when injected into mature larvae of the fleshfly, Sarcophaga peregrina. It is 25 times as active as -ecdysone when injected into diapausing pupae of the silkworm, Samia cynthia.

2. By the biological assay of hormone extracted from injected animals, it was possible to approximate the half-inactivation times of the endocrine activities provoked by the injection of -ecdysone or cyasterone.

3. In the fly larva the half-inactivation time was about 1 hour for -ecdysone and about 3-4 hours for cyasterone. Therefore, cyasterone's resistance to inactivation can fully account for its 2-fold greater activity in the larval fly.

4. In diapausing silkworm pupae the half-inactivation time was about 6 hours for -ecdysone and 32 hours for cyasterone. Consequently, cyasterone's 5-fold greater stability can only partially account for its 25-fold greater activity in the pupal silkworm.

5. The residual difference must be due to other presently unknown properties of the cyasterone molecule which further amplify its activity for silkworm pupae but not for the larval fly.