during the second phase ( the last 4 days ) , the middle part of the gland synthesis approximately 45 mg of the silk protein sericin ( 31 % serine ) and the posterior part of the gland synthesizes approximately 130 mg of the silk protein fibroin ( 46 % glycine , 29 % alanine and 12 % serine ) .
C0074529
silk
C0016042
fibroin