Sedimentation Analyses of Ribosomes and Polyribosomes from the Posterior Silk Gland of the Silkworm, Bombyx Mori.

Abstract

Sedimentation propeties of ribosomes and polyr ibosomes obtained from the posterior silk gland of the domesticated silkworm, Bombyx Mori, (Heian X Gunpaku) have beer studied.
The posterior silk glands at the fifth larval instar were homogenized in the ice cold rat liver supernatant. The homogenate was centrifuged for 10 min at 800g (average) and then deoxycholate was added to the supernatant at a final concentration of 1 %.
This supernatant was analysed by sucrose density gradient centrifugation at 40,000 rpm for 60 min. using a swing bucket rotor Hitachi RPS-40, The same material was also analysed by a Spinco Model E analytical centrifuge.
The polyribosomal patterns up to pentam er were clearly detected in the beginning of fifth larval instar (24-48 hours old). At the later stage of the same instar, the amount of polyribosomes decreased gradually and at the end of the fifth larval instar, no polyribosomal pattern was detected.
This finding is not consis tend with the rate of biosynthesis of fibroin, and it is suggested that the increase in the amount of RNase activity of the posterior silk gland at the end of the fifth larval instar is probably responsible for the disappearance of the polyribosomes.
The standard sedimentation, coefficient at infinite dilution (S⁰₂₀, w) of the ribosome monomer from the posterior silk gland was found to be 79.6 S.