Mehra R K, Coughlan M P
Arch Biochem Biophys. 1984 Mar;229(2):585-95. doi: 10.1016/0003-9861(84)90191-7.
Purine hydroxylase II from Aspergillus nidulans has been purified to near homogeneity. The enzyme has a pI of 5.7, a molecular weight of 300,000, and two subunits with molecular weight of 153,000 each. The enzyme contains 2 FAD, 2 molybdenum atoms, and 4 (2 Fe-2S) iron-sulfur centers per molecule and exhibits broad specificity for reducing and oxidizing substrates. Among the more notable characteristics are the ability to oxidize hypoxanthine and nicotinic acid but not xanthine and virtually complete inactivity with oxygen. Moreover, while the enzyme is inactivated by borate and methanol, it is very resistant to cyanide and arsenite and it not inactivated by allopurinol. At infinite concentrations of reducing and oxidizing substrates, the Km for hypoxanthine was 119 microM, for nicotinic acid was 136 microM, and for NAD+ was 525 microM.
来自构巢曲霉的嘌呤羟化酶II已被纯化至接近均一。该酶的等电点为5.7，分子量为300,000，由两个分子量均为153,000的亚基组成。每个分子的酶含有2个黄素腺嘌呤二核苷酸（FAD）、2个钼原子和4个（2铁-2硫）铁硫中心，并且对还原和氧化底物表现出广泛的特异性。其中更显著的特性包括氧化次黄嘌呤和烟酸的能力，但不能氧化黄嘌呤，并且对氧气几乎完全无活性。此外，虽然该酶会被硼酸盐和甲醇灭活，但它对氰化物和亚砷酸盐具有很强的抗性，并且不会被别嘌呤醇灭活。在还原和氧化底物浓度无限时，次黄嘌呤的米氏常数（Km）为119微摩尔，烟酸的Km为136微摩尔，烟酰胺腺嘌呤二核苷酸（NAD+）的Km为525微摩尔。
