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184 Advances in textile biotechnology

R01 R02 R03 R04 R05 R06 R07 R08 R09 R10 R11 R12

A01 A02 A03A04 A05 A06 A07 A08 A09 A10 A11

a aa a bb b aaa a a aa a a aa a b b b b c

Repetitive crystalline regions b (GAGAGY) or (GAGAGVGY)
a (GAGAGS) c (GAGAGSGAAS)
Amorphous regions consensus sequence:
TGSSGFGPYVANGGYSGYEYAWSSESDFGT
8.3 Schematic representation of the organization of the B. mori fi broin
heavy chain gene. One-letter standard amino acid abbreviations are
used (Asakura et al., 2002).

Table 8.2 Properties and composition of sericin fractionated with hot water
(Komatsu, 1979; Robson, 1985)
Fraction I II III IV Whole sericin
Content (%) 41.0 38.6 17.6 3.1 100.0
Coefficient of dissolution velocity 5.33 1.76 0.70 0.22 —

Crystallinity (%) 3.0 18.2 32.5 37.6 15.06
Total of amino acids with polar 76.30 75.29 70.69 58.97 74.61
side chains (A p )
Total of amino acids with 23.74 24.70 29.27 41.03 25.68
nonpolar side chains (A n )

together by hydrophobic bonds between the sheets. The amorphous regions
contain negatively charged, polar, bulky hydrophobic, and aromatic resi-
dues.
Sericin is distinctly different from fi broin. Bombyx mori sericin is rich in
serine, glycine, and aspartic amino acids which together comprise about
two-thirds of the total residues. There are approximately 75% of amino acid
residues with polar side chains and 25% with nonpolar side chains. Komatsu
(1979) has reported that the four stratified sericin fractions (I, II, III and

IV) form different layers from the outside to the inside to cover the fi broin
(Komatsu, 1979; Robson, 1985) (Table 8.2). These four layers constitute 41,
38.6, 17.6 and 3.1%, respectively, in content and differ in their rate of dis-
solution in hot water. Sericin I was shown to be random coil and is the most
readily soluble outer fraction. The remaining fractions, which were increas-

ingly more difficult to solubilize in hot water, showed a progressive increase

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