We have carried out b y the salting-out method, a study on the differences of the protein fractions during the larval and pupal stage of Bombyx mori. We tried to find a relationship between these data and the differences in the ribosomes as studied with the analytical ultracentrifuge and sucrose gradients. The salting-out diagrams of the unfertilized egg and the embryo, show only one peak at 65% ammonium sulphate saturation; when hatched and during the larval stages, the diagrams show 2 peaks at 50 and 75% of saturation (fig. 1). After spinning the cocoon a third peak at 65% of saturation appears, which remains during the entire pupal stage. In the female pupa of 336 hours, a peak appears at 30% of saturation; this peak, which is present also in the female moth (fig. 2), seems to be related to the growth of the eggs, since it is lacking in the male (fig. 3). With the analytical ultracentrifuge (fig. 5), one observes in the last stage of the larva a polysome peak which rapidly decreases until it disappears after metamorphosis. The ribosomes decrease quantitatively in the young pupa and increase again towards the end of the pupal stage, becoming more pronounced in the female moth. Beginning with the second larval stage the presence of a 16 S fraction can be noted in both sexes. This fraction is always abundant in the female but it decreases considerably in the male before the adult emerges. The fact, that the ribosomes and polysomes are present in relatively high concentration shortly before the appearance of the 65 % peak, suggests that the ribosomes are active in the synthesis of this fraction.
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Con il contributo del Ministero per i Beni e le Attività Culturali