色氨酸或酪氨酸作为光敏剂介导的UV-B照明可切割胱氨酸中的二硫键。,Journal of Agricultural and Food Chemistry

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色氨酸或酪氨酸作为光敏剂介导的UV-B照明可切割胱氨酸中的二硫键。
Journal of Agricultural and Food Chemistry ( IF 5.7 ) Pub Date : 2020-05-21 , DOI: 10.1021/acs.jafc.0c01760
Zichen Zhao ₁ , Mahesha M Poojary ₁ , Leif H Skibsted ₁ , Marianne N Lund _{1,

2}

Affiliation

紫外光对蛋白质中二硫键的光解会影响其结构和功能。本研究旨在研究在无氧和有氧条件下，无胱氨酸（二硫化物）与色氨酸（Trp）或酪氨酸（Tyr）的组合组成的蛋白质骨架的系统中，UV-B光对二硫化物的切割效率，并鉴定UV-B光形成的氧化产物。对于厌氧等摩尔水溶液（每个200μM； pH 7.0），光激发的Trp几乎以1：1的化学计量将胱氨酸还原为半胱氨酸（Cys），而光激发的Tyr提供较低的Cys浓度。表观量子产率的计算允许在反应效率之间进行比较，并且表明由光激发的Trp比由光激发的Tyr和单独的胱氨酸更有效地由胱氨酸的二硫键裂解形成Cys，并且Trp比Tyr对光降解更敏感。和半胱氨酸在需氧和厌氧条件下都可以。将胱氨酸和Trp之间的比例提高到1：2的比例不会增加游离硫醇形成的效率，但会导致Trp的光降解效率更高。由胱氨酸的二硫键裂解形成的游离硫醇被进一步氧化为其他未确定的化合物。胱氨酸和Trp分别以1：1和1曝光后，仅以较小浓度鉴定出Trp氧化产物（3-羟基犬尿氨酸（3-OH-Kyn）和色胺）。在需氧和厌氧条件下的比率为2，表明进一步光降解为未鉴定的化合物。3,4-二羟基苯丙氨酸（DOPA）是在有氧和厌氧条件下，以1：1的比例在光照的胱氨酸和Tyr样品中的Tyr氧化而形成的。

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Cleavage of Disulfide Bonds in Cystine by UV-B Illumination Mediated by Tryptophan or Tyrosine as Photosensitizers.

Photolytic cleavage of disulfide bonds in proteins by UV light will influence their structure and functionality. The present study aimed to investigate the efficiency of disulfide cleavage by UV-B light in a system without a protein backbone consisting of combinations of cystine (a disulfide) and tryptophan (Trp) or tyrosine (Tyr) under anaerobic and aerobic conditions and to identify oxidation products formed by UV-B light. Cystine was reduced to cysteine (Cys) almost with a 1:1 stoichiometry by photoexcited Trp for anaerobic equimolar aqueous solutions (each 200 μM; pH 7.0), while photoexcited Tyr provided lower concentrations of Cys. The calculation of apparent quantum yields allowed for a comparison between the efficiency of reactions and showed that formation of Cys from disulfide cleavage of cystine was more efficient by photoexcited Trp than by photoexcited Tyr and of cystine alone and that Trp was more sensitive to photodegradation than Tyr and cystine under both aerobic and anaerobic conditions. Increasing the ratio between cystine and Trp to a 1:2 ratio did not increase the efficiency of free thiol formation but caused a more efficient photodegradation of Trp. The free thiol formed from disulfide cleavage of cystine was further oxidized to other unidentified compounds. Trp oxidation products (3-hydroxykynurenine (3-OH-Kyn) and tryptamine) were only identified in minor concentrations following light exposure of cystine and Trp in 1:1 and 1:2 ratios under both aerobic and anaerobic conditions, indicating further photodegradation to unidentified compounds. 3,4-Dihydroxyphenylalanine (DOPA) was formed from the oxidation of Tyr in the illuminated samples of cystine and Tyr in a 1:1 ratio under both aerobic and anaerobic conditions.

更新日期：2020-06-24

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