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 pharate adult flight muscle delays eclosion, slows down the rate of thinning of the old cuticle and suppresses the cuticle degrading activity of moulting fluid. The effect of 20-hydroxyecdysone on the cuticle degrading activity of moulting fluid is dose-dependent. Also 20-hydroxyecdysone prevents the normal increase in activity of the enzyme moulting fluid protease 1 (MFP-1). The activity of another enzyme, beta-N-acetylglucosaminidase, was reduced to a much smaller extent. The effects of 20-hydroxyecdysone on MFP-1 titre and ability of moulting fluid to solubilize labelled cuticle are consistent with the hypothesis that NIFP-1 is the primary enzyme catalysing cuticle breakdown.