Fujii I, Ebizuka Y, Sankawa U
Faculty of Pharmaceutical Sciences, University of Tokyo.
J Biochem. 1988 May;103(5):878-83. doi: 10.1093/oxfordjournals.jbchem.a122365.
An enzyme activity which catalyzes the ring cleavage of the anthraquinone questin to form benzophenone desmethylsulochrin was found in the cell-free extract of Aspergillus terreus, a (+)-geodin producer. The product was identified as desmethylsulochrin by high-resolution mass spectroscopy and chemical carrier dilution analysis. The enzyme showed an absolute requirement of NADPH and molecular oxygen. Therefore, the enzyme, named questin oxygenase, was considered to be classified as a monooxygenase. The optimum pH was around 7.5. The enzyme was very unstable and lost its activity completely after storage overnight at 4 degrees C in 0.05 M phosphate buffer, pH 7.5. The instability of the questin oxygenase was partially overcome by the addition of polyols and the non-ionic detergent Tween 80 to the buffer. By DEAE-cellulose column chromatography, two protein fractions, named DE-I and DE-II, were obtained. Neither fraction reacted with questin by itself. However, the combination of DE-I and DE-II reconstituted the questin oxygenase system to convert questin to desmethylsulochrin. This result suggested that the system is not a simple combination of oxygenase and hydrolase, but requires some additional factor(s) such as electron transfer protein.
在土曲霉（一种（+）-土霉素产生菌）的无细胞提取物中发现了一种酶活性，该酶催化蒽醌化合物醌茜的环裂解形成二苯甲酮去甲基苏洛醇。通过高分辨率质谱和化学载体稀释分析鉴定该产物为去甲基苏洛醇。该酶表现出对NADPH和分子氧的绝对需求。因此，这种名为醌茜加氧酶的酶被认为属于单加氧酶。最适pH约为7.5。该酶非常不稳定，在0.05 M pH 7.5的磷酸盐缓冲液中于4℃过夜储存后完全丧失活性。通过向缓冲液中添加多元醇和非离子洗涤剂吐温80，部分克服了醌茜加氧酶的不稳定性。通过DEAE-纤维素柱色谱，得到了两个蛋白质组分，分别命名为DE-I和DE-II。单独的任何一个组分都不会与醌茜发生反应。然而，DE-I和DE-II的组合重构了醌茜加氧酶系统，将醌茜转化为去甲基苏洛醇。这一结果表明该系统不是加氧酶和水解酶的简单组合，而是需要一些额外的因子，如电子传递蛋白。
