236 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS TABLE 2--SOME AMINO ACIDS IN MILK PROTEINS •Gm. per 16 Gm. of N-- Human Cow Ewe Arginine 3.7 3.4 3.2 Histidine 2.7 2.6 2.7 Lysine 7.2 8.3 8,4 Tyrosine 5,4 6.4 Tryptophan 1.5 1.4 Phenylalanine 5.3 4.7 4.7 Cystine 1.6 0.7 Methionine 2.2 2.7 2.5 Threonine 4.5 4.5 4.3 Leucine 9.8 9.0 9.6 Isoleucine 7.5 5.7 5.5 Valine 8.8 7.0 7.4 TABLE 3--SOME AMINO ACIDS IN WHOLE ANIMALS •Gm. per 16 Gm. of N--- Rat Chicken Arginine 5.9 5.8 Histidine 1.8 1.5 Lvsine 6.1 6.3 Phenylalanine 3.4 4.2 Methionine 2.0 1.6 Threonine 3.7 3.7 Leucine 6.4 7. :2 Isoleucine 3.8 4.2 Valine 4.5 5.4 Glutamic Acid 13.9 11.6 Aspattic Acid 8.1 8.2 Glycine 10,0 11.0 tion in three of the eighteen amino acids (methionine, serine, and threonine) while turtle collagen de- viated from the majority only in threonine. Other tissue proteins such as liver, stroma, hemoglobins, etc., show remarkably similar am- ino acid patterns and if any marked differences are encountered they are usually confined to the sulfur amino acids and possibly to the hydroxyamino acids. A group of tissue proteins of ecto- dermal origin such as hair, nails, horn, feathers, etc., have been recognized for the past seventy-five years as having certain features in common. These proteins are re- sistant to digestion by pepsin and by trypsin and are insoluble in dilute acids, alkalies, water, and or- ganic solvents. They are called keratins from the Greek word "Keras," horn. Studies initiated about twenty years ago showed that keratins could be divided into two groups which had approximately the same physical properties but which differed in the molecular ratios of their basic amino acids, arginine, TABLE 4•AMINO ACIDS IN HAIR KEKATINS . Gm. per 16 Gm. of N- Human Hair Chimpanzee Hair Swine Hair Lamb's Wool Arginine 9.6 8.1 10.5 10.1 Histidine 0.9 0.6 1.1 0.9 Lysine 2.6 2.0 3.7 2.8 Tyrosine 3.1 3.3 3.4 5.5 Tryptophan 0.7 1.4 0 7 Phenylalanine 2.7 •} 6 4.0 Cystine 16.0 1• 15 13.9 13.6 Methionine 1 0 .. 0.5 0.7 Setinc 7.6 .. 9.0 Threonine 7.2 ., •' 1 6.5 Leucine .... 8.0 7.8 Isoleucine .... 4.5 4.2 Valine .. 5.7 5.1 Glutamic Acid lz[ 18 .. 17.2 15.4 Aspattic Acid 8.0 .. 7.7 7.1 Proline .... 9.3 8.0

CHEMICAL CLASSIFICATION OF KERATINS 237 histidine, and lysine. The one group comprising horn, hair, etc., were called eukeratins and yielded on acid hydrolysis histidine, lysine, and arginine in a molecular ratio of approximately 1:4:12. The other group, which did not show this ratio of basic amino acids, were designated pseudokeratins. Table 4 gives the amino acid patterns of four typical hair pro- teins. A calculation of the molecu- lar ratios of the amino acids of these four types of hair as well as many others not given in this table shows that although the majority of amino acids fall into approximately the same pattern, samples of hair from different species show marked varia- tions in the molecular ratios in one or more of the amino acids investi- gated except for the basic and acidic amino acids. Tables $ and 6 give the composi- tion of three typical horn keratins, of feathers and of two species of quills. Here again molecular ratios of the basic amino acids and of as- partic acid are relatively constant T•,sLE 6wAmNo Acres T.•sI.• 5--AMISO Acres IIg Ho•.s ,-Gm. per 16 Gin. of N--, Rhinoc- Finger Cattle eros Nails Horn Horn Arginine 10.0 8.6 8.3 Histidine 0.5 0.6 0.6 Lysine 2.8 2.4 2.7 Tyrosine .. 5.7 8.8 Tryptophan .. 0.7 1.7 Phenylalanine 3.3 5.1 Cystine 1•19 12.4 8.9 Me thionine 1.0 0.5 1.5 Serine .. . 7 Threonine .. • 3 5.1 Leucine .. 8.5 9.3 Isoleucine .. 4.4 4.8 Valine 5.6 5.7 Glutamic Acid 1•17 14.2 13.5 Aspattic Acid 8.4 7.9 9.0 Proline ...... although there appear to be differ- ences in the amounts of glutamic acid which may exceed the experi- mental errors of the analytical method. Table 7 shows the amino acid composition of dental enamel kera- tin and human skin as well as reca- pitulating the results on human hair and finger nails to facilitate compari- son. It will be seen that although the molecular ratios of the basic amino acids and methionine of den- FEATItERS AIgD Quil. l.s Hen's Feathers Gm. per 16 Gm. of N- Porcupine Quills Echidna Quills Arginine 8.0 7.7 7.2 Histidine 0.4 0.6 0.5 Lysine 1.4 2.6 1.9 Tyrosine 2.3 3.3 9.6 Tryptophan 0.7 0.9 2.7 Phenylalanine 5.5 3.6 7.2 Cystine 8.7 9.5 12.5 Methionine 0.5 0.8 1.1 Serine 10.2 6.2 6.0 Threonine 4.6 5.4 4.1 Leucine 8.5 .... Isoleucine 6.4 .... Valine 8.9 Glutamic Acid 10.4 1•18 •13 Aspattic Acid 7.5 8.8 6,9 Proline 9.4 ....