Coughlan M P, Mehra R K, Barber M J, Siegel L M
Arch Biochem Biophys. 1984 Mar;229(2):596-603. doi: 10.1016/0003-9861(84)90192-9.
Purine hydroxylase II from Aspergillus nidulans contains a molybdenum cofactor very similar to that found in a number of other molybdenum-containing hydroxylases. (A. nidulans contains two purine hydroxylases, I and II, related to each other by possession of a common cofactor and overlapping substrate specificity.) Addition of reducing substrates effects bleaching of the visible absorption spectrum of the enzyme, the decrease in absorbance at 450 nm being linearly proportional to that at 550 nm. No increase in absorption at longer wavelengths was observed during such titrations. Electron paramagnetic resonance studies of reduced samples of native and modified enzyme species showed the presence of a number of Mo(V) signals (gav = 1.97), exhibiting H hyperfine coupling, comparable to those in the corresponding enzymes from other sources. The enzyme possesses two non-heme-iron-sulfur centers, one (Fe2S2)I with gav less than 2.0 and the other (Fe2S2)II with gav greater than 2.0. The flavin radical signal observed at pH 7.8 had a linewidth of 1.5 mT, indicating it to be the anionic form FAD- . In this respect purine hydroxylase II is unique among all molybdenum-containing hydroxylases studied to date.
来自构巢曲霉的嘌呤羟化酶II含有一种钼辅因子，该辅因子与许多其他含钼羟化酶中发现的钼辅因子非常相似。（构巢曲霉含有两种嘌呤羟化酶，I和II，它们通过拥有共同的辅因子和重叠的底物特异性而相互关联。）添加还原底物会导致该酶的可见吸收光谱发生漂白，450 nm处吸光度的降低与550 nm处的降低呈线性比例关系。在这种滴定过程中，未观察到较长波长处的吸收增加。对天然和修饰酶种类的还原样品进行的电子顺磁共振研究表明存在许多Mo(V)信号（gav = 1.97），表现出H超精细耦合，与其他来源的相应酶中的信号相当。该酶拥有两个非血红素铁硫中心，一个（Fe2S2）I的gav小于2.0，另一个（Fe2S2）II的gav大于2.0。在pH 7.8观察到的黄素自由基信号的线宽为1.5 mT，表明它是阴离子形式FAD- 。在这方面，嘌呤羟化酶II在迄今为止研究的所有含钼羟化酶中是独一无二的。
