Abstract
Differences between sexes concerning the changes of uric acid and protein contents in the silkworm during its pupal stage, which have been described in a previous paper (TOJO, 1971), have also been evidenced through the following tracer studies. Active incorporation of 14C into uric acid during the 6 hours after 2-14C-glycine injection was observed in the male in the mid-pupal stage and again shortly before emergence, whereas in the female it was observed only in the late pupal stage, namely those stages coinciding well with the stages of rapid accumulation of uric acid. The incorporation of 14C into protein from injected 2-14C-glycine increases conspicuously from the mid-pupal stage, in the female, reaching a maximum at the 80% pupal durationstage. When protein was labelled with the injection of 2-14C-glycine into early male pupae, 14C was lost from the protein and appeared rapidly in the uric acid from the mid-pupal stage. In the female, 14C in both protein and uric acid changed only slightly. From the kinetic analyses of the above-mentioned tracer experiments, it was calculated that in the male, the protein synthesized during pupal period is 10% of total protein, while 37% of larval protein degrades to amino acids, causing an active catabolism to uric acid of larval protein without being reutilized. In the female, only 12% of total protein degrades to amino acid, which is efficiently reutilized for adult tissue formation. This was also shown in the investigations related to the distribution of protein among tissues in the female pupa. The above-mentioned differences between sexes are believed to be due to the small development of the testes in the male compared with the ovaries in the female. Based on a study of the changes that occur in the specific activity of protein and of free amino acids in the tissues of the female pupae that has been injected with U-14C-leucine, it can be suggested that the larval proteins are used for adult tissue formation, without being degraded to amino acids.
