Developmental pattern of thymidylate synthetase activity in the silkworm,Bombyx mori

Thymidylate synthetase activity (as expressed per mg of protein and per the whole insect) in extracts from Bombyx mori changes considerably during development. The enzyme is present in unfertilized eggs. After fertilization its activity initially increases but then decreases in parallel with the beginning of diapause. During postdiapause embryonic development the level of the enzyme quickly increases, but decreases again after hatching. In larvae the activity is low during the first instars but rises dramatically after the 4th ecdysis. The whole period of pharate pupal, pupal, and pharate adult development is characterized by a U-shaped pattern of the thymidylate synthetase activity.In order to explain some aspects of this pattern the activity of the thymidylate synthetase in extracts from some organs of the silkworm was also examined.