Urocanate

Cysteine is used as a reductant for cold wave treatment in place of thioglycoHc acid. A/-Lauroylarginine ethyl ester [48076-74-0] is appHed as the hydrochloride as a preservative. Urocanic acid [104-98-3] hich. is derived from histidine is used in skin cream as a uv absorber (235). 

The urocanic-acid-modified chitosan showed good DNA binding abihty, high protection of DNA from nuclease attack, and low cytotoxicity. The transfection efficiency of chitosan into 293T cells was much enhanced after coup-Hng with urocanic acid [96]. 

To induce immune suppression the electromagnetic energy of UV radiation must first be absorbed by an epidermal photoreceptor and then converted into a biologically recognizable signal. Three epidermal photoreceptors have been identified DNA, urocanic acid (UCA) and membrane lipids. 

Urocanic acid (2-propanoic acid 3-[lH-imidazol-4-yl] is located superficially in the stratum comeum. Metabolism of epidermal UCA does not occur in situ due to the absence of urocanase, resulting in the accumulation of UCA in the epidermis. Upon UV exposure, naturally occurring trans-UCA converts to the d.s-isomer, in a dose dependent manner, until the photostationary state is reached, when equal quantities of trans- and m-UCA are found in the skin.15 Based on an analysis of the action spectrum for UV-induced immune suppression, and the fact that no immune suppression was observed in mice whose stratum comeum was previously removed by tape stripping, De Fabo and Noonan suggested that urocanic acid was the photoreceptor for UV-induced immune suppression.16 Since the initial experiments many others have documented, the ability of ris-UCA to initiate immune suppression, documented its presence in the serum of UV-irradiated mice, and demonstrated that m-UCA plays a role in UV-induced skin cancer induction. (For a more complete review of the role of m-UCA in immune suppression see two excellent reviews by Norval and colleagues.1718)... 

Morrison, H., Photochemistry and photobiology of urocanic acid, Photo dermatology 2, 158-65, 1985. 

Norval, M. and El-Ghorr, A. A., Studies to determine the immunomodulating effects of cis-urocanic acid, Methods 28, 63-70, 2002. 

Norval, M., Gibbs, N. K., and Gilmour, J., The role of urocanic acid in UV-induced immunosuppression Recent advances (1992-1994), Photochem. Photobiol. 62, 209-217, 1995. 

Moodycliffe, A. M. et al., Differential effects of a monoclonal antibody to cis-urocanic acid on the suppression of delayed and contact hypersensitivity following ultraviolet irradiation, J. Immunol. 157, 2891-2899, 1996. 

El-Ghorr, A. A. and Norval, M., A monoclonal antibody to cis-urocanic acid prevents the UV-induced changes in Langerhans cells and DTH responses in mice, although not preventing dendritic cell accumulation in lymph nodes draining the site of irradiation and contact hypersensitivity responses, J. Invest. Dermatol. 105, 264-268, 1995. 

Kim, T. H. et al., Viability of the antigen determines whether DNA or urocanic acid act as initiator molecules for UV-induced suppression of delayed-type hypersensitivity, Photochem. Photobiol. 78, 228-234, 2003. 

Noonan, F. R, De Fabo, E. C., and Morrison, H., Cis-urocanic acid, a product formed by UVB irradiation of the skin, initiates an antigen presentation defect in splenic cells in vivo, J. Invest. Dermatol. 90, 92-99, 1988. 

Higaki, Y., Hauser, C., Siegenthaler, G., and Saurat, J. H., cis-Urocanic acid does not inhibit... 

Hurks, H. M. et al., Differential suppression of the human mixed epidermal cell lymphocyte reaction (MECLR) and mixed lymphocyte reaction (MLR) by cis-urocanic acid, Photochem Photobiol 65, 616-621,1997. 

Yarosh, D. B., Alas, L., Kibitel, A. L., and Ullrich, S. E., Urocanic acid, immunosuppressive cytokines, and the induction of human immunodeficiency virus, Photodermatol. Photoimmunol. Phtotomed. 9, 127-130, 1992. 

Zak-Prelich, M. et al., cis-Urocanic acid does not induce the expression of immunosuppressive cytokines in murine keratinocytes, Photochem. Photobiol. 73, 238-244., 2001. 

Jaksic, A. et al., Cis-urocanic acid synergizes with histamine for increased PGE2 production by human keratinocytes Link to indomethacin-inhibitable UVB-induced immunosuppression, Photochem. Photobiol. 61, 303-309, 1995. 

Hart, P. H.et al., Histamine involvement in UVB-and cis-urocanic acid-induced systemic suppression of contact hypersensitivity responses, Immunology 91, 601-608, 1997. 

The azide derivatives 269 of urocanic acid undergo thermolysis to give 270 in moderate yields, presumably via cyclization of the isocyanate and migration of the alkyl group R (Equation 53) <2002TL5879>. When R is larger than ethyl, a different ring system is formed instead. 

Porphobilinogen synthase Urocanate hydratase 3-Hydroxypalmitoyl-[ACP] dehydratase Uroporphyrinogen 111 synthase... 

A specialized amino acid residue that serves as an essesn-tial electrophilic center in several enzymatic reactions, including those catalyzed by L-phenylalanine ammonia lyase (Reaction L-phenylalanine tranx-cinnamate + NH3) and L-histidine ammonia lyase (Reaction L-histi-dine urocanate + NH3). The former facilitates the elimination of ammonia and the pro-S hydrogen of phe-nylanine, and the initial step is nucleophilic attack of... 

This enzyme [EC 4.3.1.3] (also known as histidinase, histidase, and histidine o -deaminase) catalyzes the conversion of histidine to urocanate and ammonia. See Dehydroalanine... 

Reeve, V. E., Bosnic, M., and Rozinova, E. (1993b). Carnosine (beta-alanylhistidine) protects from the suppression of contact hypersensitivity by ultraviolet B (280-320nm) radiation or by cis urocanic acid. Immumnology 78, 99-104. 

Isoguanine (94), which is found in Prioneris wings along with hypoxanthine (92), xanthine (91), and uric acid (95), shows antineoplastic activities (Table VI) (57). Isolation of urocanic acid (137) from this wing material represents the first detection of this histidine derivative in an arthropod (Table VIII). A nonpteridine pigment, xanthommatin (58) (cf. Section II,B,l,b), is found in the larval body of Pieris brassicae (Table V). 

E. Metabolism of His begins with oxidative deamination leading to production of free ammonia and the intermediate urocanic acid. 

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