[Autonomous behaviour of tryptophan-degrading enzymes during metamorphosis ofBombyx mori rb: Localization and time-course of tryptophan pyrrolase activity].

Tryptophan pyrrolase activity has been determined inBombyx mori rb in daily intervals using two different methods. Separation of kynurenine by electrophoresis and fluorimetric determination proved to be more reliable than estimation by the Bratton-Marshall procedure. 1. Maximal activity in vitro is obtained at pH 8.5 and 1.2 to 2.4 mM tryptophan. The enzyme is inhibited by higher substrate concentration. 2. In the fat body the specific activity of the enzyme follows a U-curve; it drops prior to spinning. In the gut wall, activity is detected with certainty only up to the time of pupation. In testes and ovaries the specific activity drops continuously through metamorphosis, while in developing ovaries the absolute activity increases considerably. During wing development the activity is high, but vanishes at the end of differentiation. No activity was found in Malpighian tubules, in the spinning gland, in the pupal gut, and in the eyes. There are no conclusive results for epidermal tissue, whereas muscle and nervous tissue have not been assayed at all. 2. At the onset of metamorphosis the low tryptophan pyrrolase activity is a limiting factor in tryptophan degradation. Tryptophan therefore increases strongly for a short time. From a comparison of developmental patterns of both tryptophan pyrrolase and kynurenine hydroxylase it is concluded that both enzymes are subject to independent regulation. It is postulated that their corresponding genes are localized in different regions of the genome which are of secondary importance and thus are transcribed according to local developmental programs only.