Winston G W, Eibschutz O M, Strekas T, Cederbaum A I
Biochem J. 1986 Apr 15;235(2):521-9. doi: 10.1042/bj2350521.
2-Oxo-4-thiomethylbutyric acid (OMBA) is a widely used oxygen-radical-scavenging agent and has been used for the detection of .OH-like species in a variety of systems. This scavenger reacts with other radicals and is therefore not specific for .OH. Since iron is required in most systems for the generation of OH-like species, studies were carried out to investigate the possible interaction of OMBA with iron. Fe3+ reacted with OMBA to produce complexes that gave rise to discrete spectra. Intense purple complexes, with broad absorbance maxima of 525-550 nm, were found at OMBA/Fe3+ ratios of up to 1:1, whereas red complexes with a prominent shoulder between 440 and 480 nm were found at higher OMBA/Fe3+ ratios. OMBA caused reduction of ferric iron to the ferrous state, as detected with 2,2'-bipyridyl as the indicator. This reduction occurs in the dark, can be photo-accelerated especially by light with wavelengths near the absorbance maximum of the respective complexes, and is increased as the OMBA/Fe3+ ratio is elevated. The presence of phosphate buffer quenches the purple and red ferric-ion-OMBA complexes and lowers the rate of reduction of Fe3+ by OMBA about 10-fold. The resulting ferrous-ion-OMBA-phosphate complex is very stable against autoxidation. Both the ferrous-ion-OMBA and ferric-ion-OMBA complexes reacted with H2O2, with the subsequent production of ethylene gas from OMBA. The interaction with H2O2 resulted in discrete spectral changes of both the ferrous-ion-OMBA and ferric-ion-OMBA complexes. The ferrous-ion-OMBA/H2O2 or ferric-ion-OMBA/H2O2 system appeared to produce .OH free radicals via a Fenton-type of reaction since ethylene production was inhibited by competitive OH scavengers. Ferrous-ion-OMBA complex reacted with H2O2 not only to produce ethylene from the OMBA, but also to promote the oxidation of another scavenger, ethanol. The ability of OMBA to chelate iron, to promote reduction of ferric iron and to react with H2O2 to produce potent oxidizing radicals may play a role in the lack of specificity of OMBA as a scavenger of oxygen radicals.
2-氧代-4-硫代甲基丁酸（OMBA）是一种广泛使用的氧自由基清除剂，已被用于检测各种体系中的类羟基自由基（·OH）。这种清除剂能与其他自由基反应，因此对·OH不具有特异性。由于大多数体系中生成类羟基自由基需要铁，因此开展了研究以探究OMBA与铁之间可能的相互作用。Fe³⁺与OMBA反应生成具有离散光谱的络合物。在OMBA/Fe³⁺比例高达1:1时，发现了强烈的紫色络合物，其宽吸收峰最大值在525 - 550 nm处；而在较高的OMBA/Fe³⁺比例下，发现了在440至480 nm之间有一个明显肩峰的红色络合物。以2,2'-联吡啶作为指示剂检测发现，OMBA导致三价铁还原为二价铁状态。这种还原在黑暗中发生，可被光加速，特别是被波长接近相应络合物吸收峰最大值的光加速，并且随着OMBA/Fe³⁺比例升高而增加。磷酸盐缓冲液的存在会淬灭紫色和红色的三价铁-OMBA络合物，并使OMBA还原Fe³⁺的速率降低约10倍。生成的二价铁-OMBA-磷酸盐络合物对自氧化非常稳定。二价铁-OMBA和三价铁-OMBA络合物都与H₂O₂反应，随后从OMBA产生乙烯气体。与H₂O₂的相互作用导致二价铁-OMBA和三价铁-OMBA络合物都出现离散的光谱变化。二价铁-OMBA/H₂O₂或三价铁-OMBA/H₂O₂体系似乎通过芬顿型反应产生·OH自由基，因为乙烯的产生受到竞争性·OH清除剂的抑制。二价铁-OMBA络合物与H₂O₂反应不仅从OMBA产生乙烯，还促进另一种清除剂乙醇的氧化。OMBA螯合铁、促进三价铁还原以及与H₂O₂反应产生强氧化自由基的能力可能在OMBA作为氧自由基清除剂缺乏特异性方面起作用。
