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 ....

238 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS TABLE 7--AMINO ACIDS IN KERATINS OF HUMAN ORIGIN Hair Gm. per 16 Gm. of N- Dental Nails Enamel Skin Epithelium Arginine 9.6 10.0 9.7 7.9 Histidine 0.9 0.5 0.9 1.9 Lysine 2.6 2.8 2.8 7.1 Tyrosine 3.1 .... 5.0 Tryptophan 0.7 .. 0.5 Phenylalanine 2.7 6'.•2 2.9 Cystine 16.0 1• ]9 0.6 3.5 Me thionine 1.0 1.0 1.0 1.0 Serine 7.6 .... 17.0 Threonine 7.2 .. 3.5 Glutamic Acid 14.8 1• 17 .. 15.9 Aspartic Acid 8.0 8.4 .. 8.4 Proline ...... 3.3 tal enamel keratin are very similar to those of the other human keratins, its content of phenylalanine is quite different from that of hair and its yield of cystinc is significantly lower than that of any other eukera- tin studied. It was thought of interest to investigate the qualitative amino acid composition of five ectoder- mal structures from the same individual by means of paper chro- matography. The results are sum- marized in Table 8. The sample of skin was the epithelial layer ob- tained after a mild attack of ex- foliative dermatitis. The dandruff was obtained by combing the hair and then separating the scales from pieces of hair, etc., by a fine screen. Althcugh the dandruff only weighed a few mg. after extraction of the fat with lipold solvents, suf- TABLE 8--APPROXIMATE MOLECULAR RATIOS oI• AMINO AciDS oF VARIOUS HUMAN KERATIN (ALL fROM ONE MAN) Hair Finger Nails Toe Nails Skin Epithelium Dandruff Arginine -3- * 13 + -3- 10t Histidine + 10 q- q- 17 Lysine q- 10 q- q- 15 Tyrosine q- 11 12 q- 10 Phenylalanine 10 10 12 10 11 Cystine 25 21 20 3 10 Methionine q- q- Serine + i6 i6 + Threonine q- 14 17 q- 10 Leucines q- 11 11 4- 10 Valine 15 14 13 11 10 Glycine 10 11 10 15 13 Alaninc + 14 15 q- 10 Glutamic Acid q- 10 10 q- 11 Aspattic Acid + 10 11 q- 12 Proline 25 22 23 10 24 * q- indicates presence ofamino acid with no indication as to concentration. t The lowest molar quantity of each amino acid in any of the proteins has been the value of 10 except in the case of cystine. assigned