892 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table VI Amino Acid Compositions of Untreated and Bleached Caucasian Hair Amino Acid Content in/•mol/g Amino Acid Untreated Bleached Cysteic acid 55 289 Aspartic acid 455 447 Threonine 653 642 Serine 870 820 Glutamic acid 871 868 Proline 672 700 Glycine 539 525 Alanine 471 460 • cystine 1380 1130 Valine 538 542 Isoleucine 250 247 Leucine 554 530 Tyrosine 132 120 Phenylalanine 130 119 Lysine 213 225 Histidine 63 69 Ammonia 780 870 Arginine 512 540 During bleaching some of the keratin dissolves in the reaction medium. The weight losses are, however, very small. After 4 hours' treatment of brown hair with 3% H22 at pH 10 and 35øC, the amount of extracted protein did not exceed 1% of the fiber weight. Even smaller protein extracts were recorded in the case of white hair treated under similar conditions. Although we could not yet assess the average molecular weight of the dissolved protein, its amino acid content has been determined and the results are given in Table VIII. The origin of the dissolved fraction is uncertain, as the relatively large differences in amino acid composition between the extract and the untreated hair argue against homogeneous solubilizaton. Some of the soluble protein could conceivably result from the destruction and elu- tion of the melanin-keratin complex. Such a view is strongly supported by the fact that the extracted protein contains two amino acids not [ound either in the bulk of hair or in the bleaching extract of the white hair. These are taurine and /•-alanine. Nevertheless, the major portion of the extract most probably represents peptides associated directly with the oxidized cystine. The cysteic acid residue is known to facilitate

HAIR BLEACHING 893 Table VII Amino Acid Composition of Keratin Material Dissolved During Bleaching of Brown Caucasian Hair Amino Acid Extract Amino Acid Content, % Untreated Whole Hair Cysteic acid 14.1 0.9 Taurine 0.2 ... Aspartic acid 9.2 6.0 Threonine 5.3 7.8 Serine 11.8 9.1 Glutamic acid 17.6 12.8 Proline 0.6 7.7 Glycine 7.6 4.0 Alanine 4.1 4.2 • cystine 3.7 16.8 Valine 4.9 6.3 Isoleucine 1.7 3.3 Leucine 3.9 7.1 Tyrosine 2.8 2.4 Phenylalanine 2.1 2.1 •5-Alanine 0.3 ... Lysine 3.9 3.1 Histidine 0.4 1.1 Arginine 7.8 8.9 greatly the hydrolysis of the adjacent peptide bond and thus create favorable conditions for destructive solubilization. Swelling of Bleached Hair Of the many ways in which the oxidative damage of keratin attendant upon bleaching manifests itself (deterioration of tactile properties, me- chanical weakening of the fiber, increase in alkali solubility, etc.), the in- crease in swelling represents a convenient means for the assessment of the extent of damage. This increase in swelling is brought about by changes in the bulk of the fiber, and thus is directly related to the over- all chemical modification of keratin by H,•O_o. Evidence has been presented here that of all the amino acids present in keratin, only the cystine undergoes a measurable extent of reaction with the peroxide possibly the oxidative breakdown of disulfide bonds alone would satisfactorily account for the increased swelling. However, the principal locus of the bleaching reaction, as we have learned earlier, is the melanin granule. It is conceivable that the oxidative destruction of the •nelanin granules might result in formation of discrete voids with-