Ahmad R, Armstrong D A
Int J Radiat Biol Relat Stud Phys Chem Med. 1984 Jun;45(6):607-14. doi: 10.1080/09553008414550871.
The uptake of reducing equivalents of X CO-2 by lumichrome in spectrophotometric titrations has been re-examined in the light of a recently reported extinction coefficient of 10 500 M-1 cm-1 at pH 6, which is in agreement with 10 270 +/- 100 M-1 cm-1 determined here. The average uptake was 1.8 +/- 0.1, independent of pH in the range 6.3-9.0. The major product appears to be a dihydro-alloxazine, which can be reoxidized quantitatively to lumichrome by X Br-2 radicals or by O2. As in the case of dihydroflavins, oxidation by O2 is biphasic. As in the case of flavins, a two electron reduction of lumichrome was also observed with the disulphide monoanion of lipoamide (LS X 2-), but that reduction does not go to 100 per cent yield. Contrary to our earlier conclusions, which were based on an erroneous extinction coefficient, the combination of lumichrome radicals (2 X LcH----HLc--LcH) was of relatively little (less than or equal to 20 per cent) importance, and the behaviour of lumichrome on treatment with reducing species was rather similar to that of flavins.
鉴于最近报道的在pH 6时荧光色素的消光系数为10500 M-1 cm-1，与本文测定的10270±100 M-1 cm-1一致，在分光光度滴定中，荧光色素对X CO-2还原当量的摄取已被重新研究。平均摄取量为1.8±0.1，在6.3 - 9.0范围内与pH无关。主要产物似乎是二氢异咯嗪，它可以被X Br-2自由基或O2定量地再氧化为荧光色素。与二氢黄素的情况一样，O2氧化是双相的。与黄素的情况一样，用硫辛酰胺的二硫单阴离子（LS X 2-）也观察到荧光色素的双电子还原，但该还原产率未达到100%。与我们基于错误消光系数得出的早期结论相反，荧光色素自由基（2 X LcH----HLc--LcH）的结合相对不太重要（小于或等于20%），并且荧光色素在与还原物质处理时的行为与黄素相当相似。
