Changes in amino acid pools in the silkworm, Bombyx mori during embryonic life : Alanine accumulation and its conversion to proline during diapause

Abstract

Alanine accumulated in silkworm eggs at the onset of diapause. When the eggs were kept at 4°C during diapause, this alanine was converted to glutamate, glutamine and especially proline. On resumption of development at 25°C after diapause, proline was used as an energy source for protein synthesis. In HCl-treated diapause eggs, which develop like non-diapause eggs, most amino acids showed similar developmental changes to those in eggs in resumption of embryogenesis after diapause. However, the proline level increased until the middle of embryonic development and then decreased. Continuous incubation of diapause eggs at 25°C after day 10 of oviposition caused a decrease in alanine with increases in glutamine and proline, while the levels of most other amino acids either decreased slightly or remained unchanged until day 80, when most eggs died. These results show that diapause eggs have a metabolic complex coupled with carbohydrate and amino acid metabolism inclusive of the 2-oxoglutarate-glutamate shuttle. Under conditions when embryogenesis proceeded, the level of phosphoethanolamine decreased rapidly.