Bongaerts G P, Uitzetter J, Brouns R, Vogels G D
Biochim Biophys Acta. 1978 Dec 8;527(2):348-58. doi: 10.1016/0005-2744(78)90349-2.
Uricase (urate:oxygen oxidoreductase, EC 1.7.3.3) of Bacillus fastidiosus was purified to homogeneity in a two-step procedure and was crystallized. The native molecule had a molecular weight of 145 000--150 000 and was composed of subunits of two kinds (Mr = 36 000 and 39 000) in a 1 : 1 ratio. The quaternary structure of the enzyme was reversibly altered, with concomitant loss of activity, at temperatures between 40 and 60 degrees C. No evidence was found for the involvement of metal ions or coenzymes in the uricase reaction. The enzyme was inhibited by various metal ions and by cyanide. The isoelectric point of the enzyme was 4.3, and pH optimum 9.5 and the optimal temperature 30--35 degrees C. Only uric acid was oxidized by the enzyme and 9-methyluric acid, xanthine, 8-azaxanthine and oxonic acid were competitive inhibitors. Uricase synthesis was repressed by allantoin and allantoate, even in the presence of uric acid, which induced synthesis of the enzyme. Molecular oxygen was an important environmental factor in the control of uricase synthesis, probably due to its effect, as cosubstrate in the uricase reaction, in assessing the cytoplasmic concentration of allantoin. The highest amounts of uricase, up to half of the intracellular soluble protein content, was found in cells growing under limited oxygen supply in media containing uric acid as the main substrate.
苛求芽孢杆菌的尿酸酶（尿酸：氧氧化还原酶，EC 1.7.3.3）通过两步法纯化至同质，并进行了结晶。天然分子的分子量为145000 - 150000，由两种亚基（Mr = 36000和39000）以1:1的比例组成。在40至60摄氏度之间，该酶的四级结构可逆改变，同时活性丧失。未发现金属离子或辅酶参与尿酸酶反应的证据。该酶受到各种金属离子和氰化物的抑制。该酶的等电点为4.3，最适pH为9.5，最适温度为30 - 35摄氏度。该酶仅氧化尿酸，9 - 甲基尿酸、黄嘌呤、8 - 氮杂黄嘌呤和氧肟酸是竞争性抑制剂。尿酸酶的合成受到尿囊素和尿囊酸的抑制，即使在存在诱导该酶合成的尿酸的情况下也是如此。分子氧是控制尿酸酶合成的重要环境因素，这可能是由于其作为尿酸酶反应中的共底物，在评估尿囊素的细胞质浓度方面的作用。在以尿酸作为主要底物的培养基中，在有限氧气供应下生长的细胞中发现了最高量的尿酸酶，其含量高达细胞内可溶性蛋白质含量的一半。
