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  • Title: Action spectra for the trans to cis photoisomerisation of urocanic acid in vitro and in mouse skin.
    Author: Gibbs NK, Norval M, Traynor NJ, Wolf M, Johnson BE, Crosby J.
    Journal: Photochem Photobiol; 1993 Mar; 57(3):584-90. PubMed ID: 8475193.
    Abstract:
    Urocanic acid (UCA) is a major UV chromophore in the upper layers of the skin where it is found predominantly as the trans isomer. UV irradiation induces photoisomerisation of trans-UCA to cis-UCA which has been shown to mimic some of the immunosuppressive properties of UV exposure. We examined the wavelength dependence for trans-UCA to cis-UCA photoisomerisation in vitro and in mouse skin in vivo over the spectral range 270-340 nm. The resulting action spectra were very similar with maximal effectiveness at 300-315 nm and equal activity at 270 nm and 325-330 nm, demonstrating that UVA-II radiation (320-340 nm) is efficient at UCA photoisomerisation. These action spectra differed markedly from the trans-UCA absorption spectrum in vitro and also the reported action spectrum for UV suppression of contact hypersensitivity in mice. These findings suggest that the relationship between cis-UCA formation in skin and UV-induced immunosuppression may be complex.
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