维生素B2催化维生素C的光氧化

Riboflavin-sensitized photooxidation of ascorbic acid: kinetics and amino acid effects

 

研究核黄素(维生素B2)含量和光照强度对核黄素敏感性抗坏血酸分解的影响,表明光和核黄素加速了抗坏血酸的分解。

核黄素,亚甲蓝和原卟啉IX的相对光敏活性在1-2ppm时为21151。抗坏血酸与单线态氧在pH7.5,6.04.5的反应速率常数分别为6·63×108,5·77×1085·27×108M-1s-1。 。

半胱氨酸对抗坏血酸的核黄素和亚甲蓝敏化的光氧化显示出强的抗氧化活性,并且其抗氧化作用是浓度依赖性的。浓度为0.1%的丙氨酸和苯丙氨酸对核黄素敏感的抗坏血酸光氧化具有抗氧化作用,但对亚甲蓝致敏的光氧化具有促氧化作用。

酪氨酸(0·1%)对核黄素和亚甲蓝致敏的抗坏血酸光氧化表现出强的促氧化活性。

然而,根据储存时间,色氨酸(0.1%)对抗坏血酸的光氧化显示出抗氧化或促氧化活性。

Abstract

The study on the effects of riboflavin contents and light intensity on the riboflavin-sensitized decomposition of ascorbic acid indicated that light and riboflavin accelerated the decomposition of ascorbic acid.

The relative photosensitizing activity of riboflavin, methylene blue and protoporphyrin IX was 21:15:1 at 1–2 ppm. The rate constants for reaction of ascorbic acid with singlet oxygen at pH 7·5, 6·0 and 4·5 were 6·63 × 108, 5·77 × 108 and 5·27 × 108 M1 s1, respectively.

Cysteine showed strong antioxidant activity on both riboflavin- and methylene blue-sensitized photooxidation of ascorbic acid and its antioxidant effect was concentration-dependent. Alanine and phenylalanine at 0·1% concentration showed antioxidant effects on the riboflavin-sensitized photooxidation of ascorbic acid but prooxidant effects on the methylene blue-sensitized photooxidation.

Tyrosine (0·1%) exhibited strong prooxidant activity on both the riboflavin- and methylene blue-sensitized photooxidation of ascorbic acid.

However, tryptophan (0·1%,) showed antioxidant or prooxidant activity on the photooxidation of ascorbic acid depending on the storage time.

 

Food Chemistry

Volume 53, Issue 4, 1995, Pages 397-403

Food Chemistry

Author links open overlay panelM.YJungaS.KKimbS.YKimb

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https://doi.org/10.1016/0308-8146(95)99834-MGet rights and content

Riboflavin-sensitized photooxidation of ascorbic acid: kinetics and amino acid effects - ScienceDirect  https://www.sciencedirect.com/science/article/pii/030881469599834M

 

 

核黄素光降解和光敏化作用高度依赖于氧和抗坏血酸浓度

Riboflavin Photodegradation and Photosensitizing Effects are Highly Dependent on Oxygen and Ascorbate Concentrations

抽象

核黄素(RF)是眼睛晶状体的正常成分,当暴露在光线下时会引发强烈的光敏活动。在用低于400nm的短波长辐射照射时,可能发生RF-光敏损伤。

 

然而,维生素C在正常晶状体中以高浓度存在,并且在抑制这些光敏化过程中起重要作用。使用体外简单模型,目的是更好地理解维生素C和氧浓度之间的关系对RF介导的色氨酸(Trp)光降解机制的影响,色氨酸是一种对光氧化特别敏感的靶。

在氮气下,RF分解达到其最大值,维生素CTrp光氧化可忽略不计。当增加氧气压力时,RF光降解下降并且维生素C光氧化强烈增加并且在100O 2时最大。射频诱导的Trp光降解首先随氧浓度增加,达到40μMO2,然后降低。 RFTrp降解受到维生素C的显着保护,因此在维生素C高于0.8mM的情况下,不超过20%的底物浓度被氧化。

 

根据我们的结果,我们得出结论,在正常晶状体的特定条件下,尽管存在RF,但高维生素C浓度(2mM中和UVA辐射的危害。然而,如果透镜状维生素C降低至0.8mM以下,则可能发生RF的光降解,因此Trp可能通过I型机制被光氧化。

 

Riboflavin Photodegradation and Photosensitizing Effects are Highly Dependent on Oxygen and Ascorbate Concentrations

 

Abstract

Riboflavin (RF) is a normal component of the eye lens which triggers a strong photosensitizing activity when exposed to light. Upon irradiation with short wavelength radiations below 400 nm, RF-photosensitized damage may occur.

 

However, vitamin C is present at high concentrations in the normal lens and plays an important role in inhibiting these photosensitization processes. An in vitro simple model was used with the objective of understanding better the relationships between vitamin C and oxygen concentrations on the mechanisms of RF-mediated photodegradation of tryptophan (Trp), a target particularly sensitive to photo-oxidation.

Under nitrogen, the RF decomposition reached its maximal value, and vitamin C and Trp photo-oxidation was negligible. When increasing oxygen pressure, RF photodegradation dropped and vitamin C photo-oxidation strongly increased and was maximal at 100% O2. RF-induced photodegradation of Trp first increased with oxygen concentration, up to 40 μM O2, and then decreased. RF and Trp degradation were significantly protected by vitamin C so that no more than 20% of the substrates concentration were oxidized in the presence of vitamin C higher than 0.8 mM.

 

From our results we conclude that in the specific conditions of the normal lens, the high vitamin C concentration (2 mM) is compatible with the UVA radiation hazard, despite the presence of RF. However, if lenticular vitamin C decreases below 0.8 mM, photodegradation of RF may occur and Trp may therefore be photo-oxidized by a Type-I mechanism.

 

SOURCE:

Photochemistry and Photobiology 72(6):815-820. 2000

https://doi.org/10.1562/0031-8655(2000)072<0815:RPAPEA>2.0.CO;2

No Access

Arnauld de La Rochette, Eduardo Silva, Inès Birlouez-Aragon, Marcelo Mancini, Ana-Maria Edwards, and Patrice Morlière

American Society for Photobiology

 

Riboflavin Photodegradation and Photosensitizing Effects are Highly Dependent on Oxygen and Ascorbate Concentrations | Photochemistry and Photobiology  http://www.bioone.org/doi/abs/10.1562/0031-8655%282000%29072%3C0815%3ARPAPEA%3E2.0.CO%3B2?journalCode=phot