title: Predominant synthesis of fibroin heavy and light chains on the membrane-bound polysomes prepared from the posterior silk gland of the silkworm, Bombyx mori.
abstract: Membrane-bound polysomes were prepared from the posterior silk gland of the silkworm, Bombyx mori, on the fourth to fifth day in the fifth larval instar. The polysomes, when supplemented with a soluble fraction from the posterior silk gland, exhibited the elongation reaction of the growing polypeptide-chains, but the initiation reaction of polypeptide synthesis was not demonstrated in this system. The predominant products synthesized on the membrane-bound polysomes were fibroin heavy chain (H-chain) and light chain (L-chain), while polypeptides of heterogeneous size classes were synthesized on the 105,000 X g-sedimentable polysomes. A substantial fraction of the fibroin L-chain synthesized was bound to the H-chain by disulfide bond. Most of the newly synthesized fibroin H- and L-chains on the membrane-bound polysomes were proved to be present within microsomal membrane vesicles because of their insensitivity to digestion with proteases in the absence of Triton X-100.
mesh_terms: D000818:Animals; D012831:Bombyx / Q000378:metabolism*; D002474:Cell-Free System; D002918:Chymotrypsin; D005088:Exocrine Glands / Q000378:metabolism*; D005349:Fibroins / Q000096:biosynthesis* / Q000235:genetics; D007814:Larva / Q000378:metabolism; D046911:Macromolecular Substances; D008854:Microscopy, Electron; D011132:Polyribosomes / Q000378:metabolism* / Q000648:ultrastructure; D014176:Protein Biosynthesis
chemical_list: D046911:Macromolecular Substances; D005349:Fibroins; D002918:Chymotrypsin