Kinetics of Synthesis of Fibroin in the Posterior Division of the Silk-gland of the Silkworm, Bombyx mori, L.

Abstract

THE synthesis of fibroin and secretion in the posterior division of silk-gland can be divided into three phases. (1) absorption of amino-acids; (2) synthesis of fibroin; (3) secretion of fibroin. We have tried to show that such a complex reaction is an enzyme system, by analysing the phenomenon of the incorporation of glycine labelled with carbon-14 into fibroin in vitro. A piece of the posterior division of silk-gland, 200 mgm. wet weight, 1–2 cm. long, was removed from the larva of the silkworm, Bombyx mori, during the middle period of the fifth instar, and incubated in a medium consisting of 0.5 ml. of saline solution (sodium chloride, 2.0; potassium chloride, 0.2; calcium chloride, 0.08; magnesium chloride, 0.04 per cent), 0.2 ml. of 0.2 M phosphate buffer (pH 7.4), 5 µmaoles of α-ketoglutaric acid, 210 µgm, of glycine, 140 µgm. of L-alanine, 75 µgm. of L-serine, 70 µgm. of L-tyrosine, 0.025 µc. of ¹⁴C-glycine (4.1 mc./mM) and filled with distilled water to 2.0 ml. at 31.7° C., and mildly shaken for 1 hr. After the incubation, fibroin in the gland cavity was separated from gland cells by the trichloroacetic acid method¹.