Table 1.
Amino acid (AA) composition (%) of various keratin sources.
| Amino acids | Mammalian keratin (α-keratin) |
Avian and reptilian keratin (β-keratin) |
||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Wool | Human hair | Human nails | Bull horns | Hog hair | Chicken feathers | Penguin feathers (Rachis)a | Penguin feathers (Barbs)a | Lizard claws | Avian beaksb | Avian clawsc | Turtle scutese | |
| Non-polar amino acid | ||||||||||||
| Ala | 3.3 | 5.2 | 6.5 | 7.1 | 4.2 | 8.7 | 5.6 | 4.5 | 4.8 | 6.3 | 6.1 | 3.0 |
| Gly | 4.6 | 6.6 | 6.6 | 11.6 | 4.5 | 13.7 | 10.4 | 8.2 | 28.2 | 31.3 | 30.8 | 30.3 |
| Ile | 3.2 | 3.1 | 3.9 | 4.6 | 3.8 | 3.2 | 5.1 | 5.7 | 2.4 | 1.7 | 1.7 | 1.8 |
| Leu | 7.2 | 7.1 | 9.9 | 9.3 | 8.2 | 8.3 | 12.1 | 9.6 | 3.6 | 7.3 | 5.8 | 8.1 |
| Pro | 5.7 | 9.6 | 4.1 | 2.9 | 5.9 | 9.8 | 11.3 | 12.4 | 9.1 | 9.6 | 9.4 | 10.1 |
| Val | 5.1 | 6.2 | 5.9 | 5.7 | 5.9 | 7.8 | 8.6 | 10.1 | 4.9 | 4.5 | 4.7 | 6.7 |
| Phe | 3.6 | 1.9 | 2.2 | 3.4 | 3.1 | 3.1 | 3.4 | 2.9 | 2.3 | 3.5 | 3.6 | 2.3 |
| Tyr | 5.9 | 1.2 | 2.8 | 2.0 | 3.4 | 1.4 | 4.6 | 4.7 | 4.1 | 8.6 | 9.0 | 12.7 |
| Total | 38.6 | 40.9 | 41.9 | 46.6 | 39.0 | 56.0 | 61.1 | 58.1 | 59.4 | 72.8 | 71.1 | 75.0 |
| Acidic/basic and polar amino acid | ||||||||||||
| Asp | 7.0 | 7.6 | 8.9 | 9.8 | 7.2 | 5.6 | 6.6 | 8.4 | 4.8 | 4.2 | 4.1 | 2.3 |
| Glu | 13.8 | 11.6 | 15.2 | 15.8 | 15.5 | 6.9 | 8.2 | 10.4 | 3.4 | 4.2 | 3.8 | 4.0 |
| Arg | 10.2 | 4.9 | 6.7 | 4.5 | 9.6 | 3.8 | 5.6 | 5.8 | 3.2 | 3.5 | 3.4 | 4.5 |
| His | 1.3 | 1.1 | 0.9 | 1.6 | 1.3 | 0.2 | 1.1 | 0.5 | 2.3 | 1.1 | 1.1 | 1.3 |
| Lys | 3.0 | 3.0 | 4.5 | 3.7 | 3.9 | 0.6 | 0.7 | 1.2 | 1.1 | 0.2 | 0.3 | 0.3 |
| Total | 35.3 | 28.2 | 36.2 | 35.4 | 37.5 | 17.1 | 22.2 | 26.3 | 14.8 | 13.2 | 12.7 | 12.4 |
| Neutral and polar amino acid | ||||||||||||
| Ser | 8.5 | 11.7 | 8.7 | 7.2 | 4.9 | 14.1 | 8.3 | 7.5 | 7.5 | 6.7 | 7.1 | 5.6 |
| Thr | 6.0 | 6.9 | 5.0 | 5.4 | 4.8 | 4.1 | 4.9 | 5.4 | 3.4 | 3.6 | 3.8 | 1.6 |
| Cys | 10.8 | 10.0 | 7.4 | 5.9 | 8.7 | 7.8 | 8.6 | 10.6 | 13.0 | 3.8 | 4.9d | 5.5d |
| Met | 0.6 | 2.5 | 0.8 | 0.5 | 0.6 | 0.1 | 1.0 | 1.7 | 0.8 | 0.8 | 0.5 | 0.1 |
| Total | 25.9 | 31.1 | 21.9 | 19.0 | 19.0 | 26.1 | 22.8 | 25.2 | 24.7 | 14.9 | 16.3 | 12.8 |
| Ref. | (Zoccola et al., 2009) | (Hill et al., 2010) | (Edwards et al., 1998) | (Edwards et al., 1998) | (Esteban et al., 2010) | (Harrap and Woods, 1964) | (Murphy et al., 1990) | (Murphy et al., 1990) | (Gillespie et al., 1982) | (Frenkel and Gillespie, 1976) | (Frenkel and Gillespie, 1976) | (Frenkel and Gillespie, 1976) |
a
Data from penguin Pygoscelis antarctica, and calculated as μmol/g to composition (%) (w/w) according to the molar mass of amino acids.
b
Kookaburra beak keratin.
c
Zinc-precipitable protein isolated from Avian claw (Kookaburra claw).
d
Content of cysteine, determined as S-carboxymethyl cysteine.
e
Zinc-precipitable protein isolated from turtle scute (Chelonia mydas).