Action spectra for the trans to cis photoisomerisation of urocanic acid in vitro and in mouse skin.
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.
Gibbs
N K
NK
Photobiology Unit, Ninewells Hospital, University of Dundee, Scotland.
Norval
M
M
Traynor
N J
NJ
Wolf
M
M
Johnson
B E
BE
Crosby
J
J
D000818:Animals; D005260:Female; D007536:Isomerism; D051379:Mice; D008812:Mice, Hairless; D012867:Skin / Q000528:radiation effects*; D014466:Ultraviolet Rays; D014560:Urocanic Acid / Q000528:radiation effects*
D014560:Urocanic Acid