title: Influence of human serum albumin on photodegradation of folic acid in solution.
abstract: 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.
authors.affiliation: Department of Radiation Biology, Institute for Cancer Research, The Norwegian Radium Hospital, Oslo, Norway.
authors.forename: Pavel
authors.initials: P
authors.lastname: Vorobey
authors.forename: Arnfinn Engeset
authors.initials: AE
authors.lastname: Steindal
authors.forename: Morten Kristian
authors.initials: MK
authors.lastname: Off
authors.forename: Alexander
authors.initials: A
authors.lastname: Vorobey
authors.forename: Johan
authors.initials: J
authors.lastname: Moan
mesh_terms: D005492:Folic Acid / Q000378:metabolism / Q000528:radiation effects*; D006801:Humans; D010100:Oxygen; D010782:Photolysis / Q000187:drug effects*; D012709:Serum Albumin / Q000494:pharmacology*; D012996:Solutions; D014466:Ultraviolet Rays / Q000009:adverse effects
chemical_list: D012709:Serum Albumin; D012996:Solutions; D005492:Folic Acid; D010100:Oxygen