Photoinduced Generation of H₂O₂ and O₂•^- by 6-formylpterin in Aqueous Solutions

Abstract

Abstract6-Formylpterin is one of the oxidized pterins that accumulate in the white skin patches of patients affected by vitiligo. Studies of photoinduced generation of hydrogen peroxide (H 2 0 2 ) and superoxide anion radical (0 2 · ) by formylpterin in acidic and alkaline aqueous solutions at 350 nm and room temperature have been performed. The photochemical processes were followed by UV-V1S spectrophotometry and enzymatic methods for H 2 0 2 and 0 2 *~determination. When formylpterin is irradiated a red intermediate, that has been proposed to be 6-carboxy-5,8-dihydropterin, is generated in an 0 2 -independent process. In the presence of air that intermediate reacts with 0 2 to yield H 2 0 2 and 6-carboxyptcrin. In anaerobic conditions it undergoes a thermal 0 2 -independent reaction which leads to a non-identified product without generation of H 2 0 2 . The rate constants of such a process were determined to be 0.011 min 1 and 0.044 min 1 at pH 5.4 and 10.5, respectively. (0 2 · ), is also generated during photooxidation of formylpterin, probably as a consequence of the electron transfer from the red intermediate to 0 2 . The biomedical importance of photoinduced generation of H 2 0 2 and 0 2 · is discussed.

New Results on the Photochemistry of Biopterin and Neopterin in Aqueous Solution

“…It has been reported that 5,8‐dihydropterins are not stable in anaerobic conditions and tautomerize to 7,8‐dihydropterin derivatives (27). In addition, the photoproduct generated during the anaerobic irradiation of FPT, which was proposed to be 6‐carboxy‐5,8‐dihydropterin (28,29), undergoes, in the absence of O 2 , a thermal reaction, in which H 2 O 2 is not generated (24). The corresponding products were not identified.…”

“…On the other hand, at longer irradiation times, the H 2 O 2 formed is higher than the FPT generated and is even higher than the consumption of the reactant. This fact very likely is due to the photo-oxidation of FPT to yield CPT and H 2 O 2 (24).…”

Development of a high-performance liquid chromatography – Tandem mass spectrometry urinary pterinomics workflow

“…In recent years, these efforts have expanded to include the aromatic pteridines derived from folic acid catabolism [12], including 6-formylpterin, 6-carboxypterin, 6-hydroxymethylpterin, pterin, and isoxanthopterin [13]. Aromatic pteridines, and to lesser extents their semi-reduced and reduced counterparts, have remarkable photocatalytic and oxidoreductive properties, including a considerable capacity to generate reactive oxygen species [14][15][16][17] and even photosensitize important biomolecules including DNA [18][19][20], folic acid [21], and tryptophan [22], which has led researchers to postulate that pteridines may actively participate in molecular pathology [13].…”

Photoinactivation of tyrosinase sensitized by folic acid photoproducts

“…Taking into account that Cap is less efficient photosensitizer than Fop, it is expected that the rate of enzyme photoinactivation should be lower when the Fop concentration decreases as a function of irradiation time. In order to elucidate the reason of the kinetic behavior of the enzyme inactivation when Fop is used as photosensitizer, and taking into account that under UV-A radiation Fop generates one molecule of H 2 O 2 for each molecule of Fop consumed (Scheme 1) [48], it was appropriate to explore the stability of tyrosinase in the presence of H 2 O 2 (see next section).…”