Occurrence of an active regulatory mechanism of protein synthesis during starvation and refeeding in Bombyx mori fat body.

The origin of the amino acids which participate in protein synthesis at the recovery from starvation have been determined in the fat body from Bombyx mori larvae. Endogeneous amino acids have been labelled with [3H] leucine and ingested ones with [14C] leucine, allowing their discrimination in the organism. 22 minutes after refeeding, proteosynthetic activity of the fat body, estimated by the polysome level, is increased 2.5 fold. Endogeneous leucine represents more than 90 p. cent of the leucine present in nascent polypeptides. Free leucine pools of the fat body and of hemolymph increase, mainly through the release of endogeneous leucine. It is therefore concluded that refeeding with amino acids induces the production of a signal or critical factor, responsible for the increase in proteosynthetic activity in the fat body.