It is likely that the major role of L-chain is to prevent the retention of H-chain in ER by forming the disulfide linkage. Silk fibroin elementary unit consists in a disulfide-linked heavy and light chain and a p25 glycoprotein in molar ratios of 6:6:1. This results in a complex of approximately 2.3 MDa. Produced exclusively in the posterior (PSG) section of silk glands, which are essentially modified salivary glands. Expressed in the posterior silk glands throughout the penultimate and last larval instars. Declines in immobile pupae and disappears within the next 12 hours when insects pupate. Partially N-terminally processed to yield a short form which lacks the first two residues of the long form. The interchain disulfide bridge is essential for the intracellular transport and secretion of fibroin.