Tryptophan oxidation photosensitized by pterin
Andrés H Thomas1, Mariana P Serrano, Virginie Rahal
1Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas, Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CCT La Plata-CONICET, Boulevard 113 y 64, 1900 La Plata, Argentina.
Free Radical Biology & Medicine
|June 11, 2013
Summary
Pterin (Ptr) photosensitizes tryptophan (Trp) oxidation via a Type I mechanism, not singlet oxygen. This electron transfer process damages amino acids, with hydrogen peroxide as a byproduct.
Area of Science:
- Photochemistry
- Biochemistry
- Molecular Biology
Background:
- Pterins are cellular components known to photosensitize DNA and nucleotide oxidation under UV-A light.
- Tryptophan (Trp) is a key amino acid and a model for studying biomolecule photooxidation.
Purpose of the Study:
- To investigate the photosensitizing ability of pterin (Ptr) on amino acid oxidation.
- To elucidate the mechanism of pterin-induced tryptophan (Trp) photooxidation.
Main Methods:
- UV-A irradiation (350 nm) of pterin and tryptophan in aqueous solutions.
- Analysis of pterin and tryptophan consumption and hydrogen peroxide production.
- Investigation of reaction mechanisms using oxygen-saturated and aerated solutions.
- Identification of tryptophan reaction products using UPLC-mass spectrometry.
Main Results:
- Pterin photosensitized tryptophan consumption without significant pterin degradation.
- Hydrogen peroxide was produced during the irradiation process.
- Tryptophan oxidation was inhibited in oxygen-saturated solutions, ruling out singlet oxygen as the primary oxidant.
- Type I photooxidation, involving electron transfer from tryptophan to the excited pterin triplet state, was identified as the main mechanism.
- Identified tryptophan reaction products supported the proposed electron transfer mechanism.
Conclusions:
- Pterin acts as a photosensitizer for tryptophan oxidation through a Type I mechanism.
- The primary pathway involves electron transfer from tryptophan to the excited pterin triplet state.
- This study reveals a novel photooxidative pathway for amino acids mediated by pterins.
![Radiosynthesis of 1-(2-[18F]Fluoroethyl)-L-Tryptophan using a One-pot, Two-step Protocol](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F63025.jpg&w=3840&q=50)
![Cercosporin-Photocatalyzed [4+1]- and [4+2]-Annulations of Azoalkenes Under Mild Conditions](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F60786.jpg&w=3840&q=50)
Related Concept Videos
01:22Photosystem II
The multi-protein complex photosystem II (PS II) harvests photons and transfers their energy through its bound pigments to its reaction center, and ultimately to photosystem I (PSI) through the electron transport chain. The pigments responsible for caputirng the light energy in photosystems include chlorophyll a, chlorophyll b, and carotenoids.
The pigment molecules are arranged across two photosystem domains — the antenna complex and the reaction center. The main aim of the pigment molecules...
The pigment molecules are arranged across two photosystem domains — the antenna complex and the reaction center. The main aim of the pigment molecules...
01:22Photoreceptors and Visual Pathways
At the molecular level, visual signals trigger transformations in photopigment molecules, resulting in changes in the photoreceptor cell's membrane potential. The photon's energy level is denoted by its wavelength, with each specific wavelength of visible light associated with a distinct color. The spectral range of visible light, classified as electromagnetic radiation, spans from 380 to 720 nm. Electromagnetic radiation wavelengths exceeding 720 nm fall under the infrared category, whereas...
01:27Photosystem I
Although structurally similar to photosystem II (PSII), photosystem I (PSI) is has a different electron supplier and electron acceptor.
Both these photosystems work in concert. An excited electron from PSII is relayed to PSI via an electron transport chain in the thylakoid membrane of the chloroplast, which is comprised of the carrier molecule plastoquinone, the dual-protein cytochrome complex, and plastocyanin. As electrons move between PSII and PSI, they lose energy and must be re-energized...
Both these photosystems work in concert. An excited electron from PSII is relayed to PSI via an electron transport chain in the thylakoid membrane of the chloroplast, which is comprised of the carrier molecule plastoquinone, the dual-protein cytochrome complex, and plastocyanin. As electrons move between PSII and PSI, they lose energy and must be re-energized...
01:29The Photochemical Reaction Center
Reaction centers are pigment-protein complexes that initiate energy conversion from photons to chemical entities. Therefore, photochemical reaction center is a more appropriate term that describes these complexes. The Nobel laureates Robert Emerson and William Arnold provided the first experimental evidence of photochemical reaction centers by demonstrating the participation of nearly 2,500 chlorophyll molecules for the release of just one molecule of oxygen. Despite thousands of photosynthetic...
01:26Oxygenic Photosynthesis
Oxygenic photosynthesis is a fundamental process in which light energy is harnessed to drive the oxidation of water, leading to the production of molecular oxygen (O₂), adenosine triphosphate (ATP), and nicotinamide adenine dinucleotide phosphate (NADPH). This process is essential for sustaining aerobic life on Earth and is primarily carried out by cyanobacteria, algae, and plants. The core of oxygenic photosynthesis lies in the thylakoid membranes, where chlorophyll pigments facilitate light...
01:34The Z-Scheme of Electron Transport in Photosynthesis
The light reactions of photosynthesis assume a linear flow of electrons from water to NADP+. During this process, light energy drives the splitting of water molecules to produce oxygen. However, oxidation of water molecules is a thermodynamically unfavorable reaction and requires a strong oxidizing agent. This is accomplished by the first product of light reactions: oxidized P680 (or P680+), the most powerful oxidizing agent known in biology. The oxidized P680 that acquires an electron from the...