- The silk of Bombyx mori is composed of the proteins fibroin and sericin, matter such as fats, wax, sand pigments plus minerals.
- Fibroin in the Bombyx mori comprises a high content of the amino acids glycine and alanine, 42.8 g and 32.4 g respectively
- The key amino acids in sericin are serine (30.1 g), threonine (8.5 g), aspartic acid (16.8 g) and glutamic acid (10.1 g)
Sericin is a complex protein composed of three distinct components (I, II and III) of which sericin III is the interior layer directly adjacent to the fibroin core. The sericin I outer lay is the most soluble of the three constituents, while sericin III is difficult to dissolve. Viewed as a cross section, the brins have the appearance of equilateral triangles with rounded corners that face each other at their respective bases.
When the brin is crushed, it splinters into numerous minute fibrils revealing the actual structure of the brins. The thickness of each fibril is less than one micron and they are parallel to the axis of the fibre. A single fibril contains many microfibrils which, when examined with an electron microscope, have a diameter of approximately 100 Å per microfibril. Microfibrils contain micelles, which are separated into crystalline and amorphous segments.