Woolfolk C A, Downard J S
J Bacteriol. 1978 Aug;135(2):422-8. doi: 10.1128/jb.135.2.422-428.1978.
Arthrobacter S-2, originally isolated by enrichment on xanthine, produced high levels of xanthine oxidase activity, requiring as little as a 20-fold purification to approach homogeneity with some preparations. Molecular oxygen, ferricyanide, and 2,6-dichlorophenol-indophenol served as electron acceptors, but nicotinamide adenine dinucleotide did not. The enzyme was relatively specific when compared with previously studied xanthine-oxidizing enzymes, but at least one purine was observed to be oxidized at each of the three positions of the purine ring that have been subject to oxidation by this type of enzyme. The enzyme had a relatively high Km for xanthine (1.3 X 10(-4) M), and substrate inhibition was not observed with this compound, in contrast to the enzyme from cow's milk. In fact, an opposite effect was observed, and double-reciprocal plots with xanthine as the variable substrate showed a concave downward deviation at high concentrations. At 2.5 mM xanthine the enzyme had a specific activity approximately 50 times that of the most active preparations of the milk enzyme. The spectrum of the Arthrobacter enzyme resembled that of milk xanthine oxidase, suggesting a similarity of the prosthetic centers of the two enzymes. The bacterial enzyme was relatively small and may be dimeric, with approximate native and subunit molecular weights of 146,000 and 79,000, respectively.
节杆菌S-2最初是通过在黄嘌呤上富集培养而分离得到的，它产生高水平的黄嘌呤氧化酶活性，某些制剂只需进行20倍的纯化就能接近均一性。分子氧、铁氰化物和2,6-二氯酚靛酚可作为电子受体，但烟酰胺腺嘌呤二核苷酸不能。与先前研究的黄嘌呤氧化酶相比，该酶具有相对特异性，但在嘌呤环上可被这类酶氧化的三个位置中的每一个位置，至少都观察到一种嘌呤被氧化。该酶对黄嘌呤的Km值相对较高（1.3×10⁻⁴ M），与牛奶中的酶不同，该化合物未观察到底物抑制现象。事实上，观察到了相反的效果，以黄嘌呤作为可变底物的双倒数图在高浓度时显示出向下凹陷的偏差。在2.5 mM黄嘌呤时，该酶的比活性约为牛奶酶最活跃制剂的50倍。节杆菌酶的光谱与牛奶黄嘌呤氧化酶的光谱相似，表明这两种酶的辅基中心相似。该细菌酶相对较小，可能是二聚体，天然分子量和亚基分子量分别约为146,000和79,000。
