MOLTING FLUID ENZYMES OF THE TOBACCO HORNWORM, MANDUCA-SEXTA - INHIBITORY EFFECT OF 20-HYDROXYECDYSONE ON THE ACTIVITY OF THE CUTICLE DEGRADING ENZYME MFP-1

The moulting process of Manduca sexta is regulated by the ecdysteroid hormone 20-hydroxyecdysone. Injection of 20-hydroxyecdysone into phara te adult flight muscle delays eclosion, slows down the rate of thinnin g of the old cuticle and suppresses the cuticle degrading activity of moulting fluid. The effect of 20-hydroxyecdysone on the cuticle degrad ing activity of moulting fluid is dose-dependent. Also 20-hydroxyecdys one prevents the normal increase in activity of the enzyme moulting fl uid protease 1 (MFP-1). The activity of another enzyme, beta-N-acetylg lucosaminidase, was reduced to a much smaller extent. The effects of 2 0-hydroxyecdysone on MFP-1 titre and ability of moulting fluid to solu bilize labelled cuticle are consistent with the hypothesis that NIFP-1 is the primary enzyme catalysing cuticle breakdown.