[Kynurenine-3-hydroxylase during metamorphosis ofBombyx mori rb: Tissue and stage specific changes in activity].

Specific activity of the enzyme, kynurenine-3-hydroxylase, has been measured in different tissues of theBombyx mori mutantrb during metamorphosis. The error of measurement was high because of the small amounts of the enzyme present (0.01-0.1 mU/mg protein in most tissues). 1. The highest activity (2 mU/mg protein) appears in Malpighian tubules two days before the onset of spinning. It vanishes completely within a few days and is only partly restored at the end of the pupal stage. 2. In larval fat body the enzyme is found in moderate amounts. Activity in the pupal stage was variable in different series of experiments; it may be correlated to macroscopic changes of the fat body. 3. Activity in larval epidermis is extremely low and may be due to contamination. No activity at any stage is detected in wing epidermis. 4. While testes never contain the enzyme, it becomes increasingly active in growing ovaries. The activity disappears during pigmentation of diapause eggs. 5. Activity has also been found in the spinning gland, in pupal heart tissue (heart tissue was not dissected at other stages), and in developing eyes. 6. The pattern and time course of hydroxylase activity suggest, that formation of the enzyme is not subject to regulation by substrate or tryptophan levels, but directed by differential gene activation.