OXYRADICALS FROM PHOTOIRRADIATED HAIR 175 10 350 400 450 500 550 Wavelength (nm) Figure 3. HTA produced from irradiated wool keratin: 0.1 g wool keratin powder in 2 mM TA phosphate buffer, pH 7.6 (phosphate buffer), irradiated for 30 min. a. No additives. b. Sodium azide added (10 mM). c. Ethanol added (! M). hair or melanin isolated from brown hair. The difference is illustrated in Figure 2 for the two types of hair. Results of previous studies indicate that oxygen consumption rates are similar for pheo- and eumelanin (32,33). This result, coupled with the results of the intrinsic ESR signals, would seem to predict greater photoinduced oxyradical production from eumelanin than from pheomelanin, in contrast to the above observation that red hair and red hair melanin give a higher overall yield of oxyradicals. Thus, while the initial rate of production of oxyradicals may be similar, or even higher, for eumelanin, the fate of these radicals must be different for the two types of melanin/hair. These apparent differences in reactivity may be explained in terms of the different structures of the two types of melanin. Brown hair contains eumelanin that is oxidized enzymatically from tyrosine. Pheomelanin formation includes the cyclization and oxidative polymerization of 5-S-

176 JOURNAL OF COSMETIC SCIENCE 12 10 0 a b c d Figure 4. HTA production from human hair: 0.2 g hair (1-mm long) in 2 ml of 2 mM TA at pH 7.6, irradiated for 90 min. a. Brown hair. b. Blond hair. c. Red hair. d. Bleached hair. cysteinyldopa and its isomers (present in smaller quantities) (34). It would appear from photobleaching studies that the sulfur-containing benzothiazine unit of pheomelanin is more resistant to oxidation than the indolic units of eumelanin (35). Therefore, eumela- nin seems to be more efficient than pheomelanin as a scavenger of reduced oxygen species. Hence the amount of 02 ß -/OH' that is available to reach the spin traps (DMPO or TA) (Figures 4, 6 reference 25) is greater for red hair and red hair melanin. The greater ability to scavenge free radicals for eumelanin suggests that the eumelanin has a better photoprotective effect with regard to hair structure than pheomelanin. This is consistent with the fact that brown hair is more easily photobleached than either red (35) or black hair (36). As shown from the experiments with wool keratin (Figure 3), the structural component of hair produces oxyradicals even in the absence of melanin. In addition to carbon- and oxygen-centered radicals, it has been reported that sulfur-centered radicals were also produced from irradiated wool keratin (17). This involves thiyl radicals, generated via