Vorobey Pavel, Steindal Arnfinn Engeset, Off Morten Kristian, Vorobey Alexander, Moan Johan
Department of Radiation Biology, Institute for Cancer Research, The Norwegian Radium Hospital, Oslo, Norway.
Photochem Photobiol. 2006 May-Jun;82(3):817-22. doi: 10.1562/2005-11-23-RA-739.
It has been proposed that photodegradation of folates may be the reason for the pigmentation of races living under high fluence rates of ultraviolet radiation. The photodegradation of folic acid (FA) induced by ultraviolet-A (UV-A) radiation, in solution and in the presence of human serum albumin (HSA), was studied with absorption and fluorescence spectroscopy. FA photodegradation, with formation of p-aminobenzoyl-l-glutamic acid, 6-formylpterin and pterin-6-carboxylic acid, was found to follow an exponential trend. A scheme of FA photodegradation, which involves photosensitization of FA degradation by its photoproducts, was proposed. The rate of FA photodegradation decreased drastically in the presence of HSA, whereas the spectral characteristics of the photoproducts remained constant. The reduction of the FA photodegradation rate by HSA was accompanied by degradation of tryptophan in HSA. Tryptophan, when added to solutions of FA, had a similar effect as HSA. In solutions of FA and HSA the FA photoproducts cause photodamage mainly to HSA rather than to FA itself. The oxygen dependence of FA photodegradation and the inhibition of this process by sodium azide indicate that singlet oxygen may participate in the photosensitizing activity of FA photoproducts.
有人提出，叶酸的光降解可能是生活在高紫外线辐射通量率下的种族色素沉着的原因。利用吸收光谱和荧光光谱研究了在溶液中以及在人血清白蛋白（HSA）存在下，紫外线-A（UV-A）辐射诱导的叶酸（FA）光降解。发现FA光降解生成对氨基苯甲酰-L-谷氨酸、6-甲酰蝶呤和蝶呤-6-羧酸，呈指数趋势。提出了一种FA光降解机制，该机制涉及FA光降解产物对FA降解的光敏化作用。在HSA存在下，FA光降解速率急剧下降，而光降解产物的光谱特征保持不变。HSA降低FA光降解速率的同时伴随着HSA中色氨酸的降解。色氨酸添加到FA溶液中时，具有与HSA类似的效果。在FA和HSA溶液中，FA光降解产物主要对HSA造成光损伤，而不是对FA本身。FA光降解对氧气的依赖性以及叠氮化钠对该过程的抑制表明单线态氧可能参与了FA光降解产物的光敏化活性。
