The Melanins

If lighter colors than these are desired it is necessary to decolorize all the melanin in the hair in a preliminary step, and then add color back to the desired depth in a second treatment. This is known as a double-process treatment. The decolorization step consists of treating the hair with an alkaline mixture of persulfate salts and peroxide. The persulfate is added to the peroxide as a dry powder immediately before applying to the hair. Although the persulfate salts alone do not have any bleaching effect, the persulfate—peroxide mixture can remove all the melanin in the hair. Dark brown or darker hair can be lightened to a light blonde shade in about an hour. 

Heavily pigmented wools such as karakul require a more stringent approach, known as mordant bleaching, in which a metal salt is first appHed. The metal cations ate preferentially absorbed by the melanin pigment, where they subsequendy decompose hydrogen peroxide to produce highly aggressive hydroxyl free radicals, which then attack and bleach the melanin (114). 

Generally, the phenotype that predisposes an individual to an increased risk of skin cancer is red or blond hair, blue eyes, and fair skin. These characteristics are surrogate measure of the sensitivity of the skin to sun exposure and the tendency to develop nevi, freckles, and sunburns based on the skin type. Freckles, which may appear abruptly after the first high dose of UV radiation sun exposure, represent clones of mutated melanocytes, and their presence is associated with an increased risk of melanoma.12 The Fitzpatrick classification of skin type is used to determine the response pattern of the skin to UV radiation and assess the risk for melanoma. There are six Fitzpatrick skin types Type I skin always burns and never tans, type II skin burns easily and tans rarely, type III skin burns sometimes and tans usually, type IV skin burns rarely and always tans, type V skin always tans and is moderately pigmented (brown), and type VI skin always tans and is darkly pigmented (black). Fitzpatrick I and II skin types are commonly affected by NMSC and MM. The susceptibility to skin cancer, both NMSC and MM, is related to the melanin content of the skin and the skin s response to UV radiation. 

Saito, Y., Cheng, M., Leslie, F. M. Civelh, O. (2001). Expression of the melanin-concentrating hormone (MCH) receptor mRNA in the rat brain. J. Comp. Neurol 435, 26-40. 

Very recently, the method has been used for the synthesis of racemic linderol A [311], a natural product isolated from the fresh bark of Lindera umbellata. This compound is reported to exhibit potent inhibitory activity on the melanin biosynthesis of cultured B-16 melanoma cells in guinea pigs, without causing any cytotoxicity in the cultured cell or skin irritation [312]. 

Furthermore, following concerns over the way the ozone layer is being damaged by man-made chemicals, some UV-c now reaches the Earth s surface, particularly in Australasia and some parts of South America. People living in such places are not adequately protected against the harmful effects of the sun s rays by the melanin in their skin. 

In the present paper we describe the catalytic mechanisms of synthetic polymer-Cu complexes a catalytic interaction between the metal ions which attached to a polymer chain at high concentration and an environmental effect of polymer surrounding Cu ions. In the latter half, the catalytic behavior is compared with the specific one of tyrosinase enzyme in the melanin-formation reaction which is a multi-step reaction. To the following polymers Cu ions are combined. 

Oxidative polymerization of phenol derivatives is also important pathway in vivo, and one example is the formation of melanin from tyrosine catalyzed by the Cu enzyme, tyrosinase. The pathway from tyrosine to melanin is described by Raper (7) and Mason (8) as Scheme 8 the oxygenation of tyrosine to 4-(3,4-dihydro-xyphenyl)-L-alanin (dopa), its subsequent oxidation to dopaqui-none, its oxidative cyclization to dopachrome and succeeding decarboxylation to 5,6-dihydroxyindole, and the oxidative coupling of the products leads to the melanin polymer. The oxidation of dopa to melanin was attempted here by using Cu as the catalyst. 

This acceleration by PIPo was restricted in the process of dopa oxidation to the quinone and was not observed in the melanin formation process. Thus the catalytic behavior of the PIPo-Cu... 

Suryanarayanan TS et al.. Characterization of the melanin pigment of a cosmopolitan fungal endophyte, Mycol Res 108 974—978, 2004. 

As the melanin structure grows, it becomes more colored giving various shades of brown color to our skin. This brown coloration acts to help protect deeper skin elements from being damaged by the UV radiation. The absence of the enzyme tyrosinase that converts tyrosine to melanin can lead to albinism. 

Tricyclazole is reported to inhibit the melanin biosynthesis pathway between 1,3,8 trihydoxynaphthalene and vermelone whereas chromatographic analysis of P. oryzae culture media indicates that KTU 3616 treatment stimulates the accumulation of the intermediate, scytalone. 

With tyrosinase, on the contrary, a two-electron oxidation occurs, as no EPR signal was detected in the catechol oxidation at pH 5.3 Melanins are polymerization products of tyrosine, whereby tyrosinase catalyses the first steps the formation of dopa (3,4-dihydroxyphenylalanine) and of dopaquinone, leading to an indolequi-none polymer The peroxidase mechanism for the conversion of tyrosine into dopa in melanogenesis was not substantiated In natural and synthetic melanins free radicals of a semiquinone type were detected by EPR 4-10 x 10 spins g of a hydrated suspension (the material was modified on drying and the number of free spins increased). The fairly symmetrical EPR signal had a g-value of 2.004 and a line-width of 4-10 G The melanins seem to be natural radical scavengers. 

The aminochromes are intermediates in the formation of the dark pigments known as the melanins, i.e. the final products of catecholamine oxidation. However, aminochromes can be converted into melanins both by oxidative and non-oxidative processes (see Section V, A). 

There are no reports in the literature of the formation of pyrrole derivatives by the oxidative degradation of the o-quinone rings of the simple aminochromes. However, several pyrrolecarboxylic acids have been obtained on oxidation of the melanins, which are considered by some authors to contain aminochrome units in the polymer (cf. ref. 168), (see Section V, A), and pyrrole-2,3,5-tricarboxylic acid has been... 

The principal pigment of human skin, hair, and eyes is melanin, which is synthesized in specialized cells, the melanocytes. They lie between the epidermis (outer layer) and the dermis (inner layer) as shown in Box 8-F. Melanocytes originate from embryonic nervous tissue and migrate into the skin by the third month of fetal life. They retain the highly branched morphology of neurons. Persons of different races all have the same numbers of melanocytes but the numbers and sizes of the pigmented melanosomes (Box 8-F) vary as does the content and chemical composition of the melanin.a d Melanosomes not only are found in the dendrites of the melanocytes but are transferred from them into adjacent epithelial cells.6 1... 

If gluten flour (40 per cent gluten) is used instead of ordinary flour, the procedure is approximately the same. A 5-lb. sack of gluten flour is washed to remove the starch. The wet gluten is placed in a 6-1. Pyrex flask with 3500 cc. of concentrated hydrochloric acid (sp. gr. 1.19) and the hydrolysis is carried out as described above. After the hydrolysis and removal of the melanin by filtration, the solution is concentrated to about 1300 cc. The glutamic acid hydrochloride is then precipitated as already described. After two recrystallizations, the yield is 180-190 g. From the mother liquors a further yield of 45-50 g, is obtained, making a total of 225-230 g. 

Glidine, a commercial diabetic food which is prepared from wheat flour and contains over go per cent of protein, may be used as a satisfactory source of glutamic acid. If this is used, it is not necessary to wash in order to remove the starch. From 1130 g. of this material, by hydrolyzing with 2500 cc. of concentrated hydrochloric acid and working up as before, 275-285 g. of glutamic acid hydrochloride may be obtained. Usually, the product from glidine is more difficult to decolorize. It has been found that an ether extraction of the hydrolysis mixture, after removal of the melanin, improves the color of the final product. 

In beagle dogs, intravenously injected radium-226 was deposited in the melanin granules of pigmented cells and rodlike organelles of the tapetum in the eye (a structure that humans do not have). Retention in the eye varied inversely with dose. At doses from 0.062 to 1.1 pCi/kg (2.3 to 41 kBq/kg), loss of pigment at the higher doses and melanosis and intraocular melanoma formation at the lower doses were observed (Taylor et al. 1972). 

---