Krafft T, Macy J M
Department of Microbiology, La Trobe University, Bundoora, Victoria, Australia.
Eur J Biochem. 1998 Aug 1;255(3):647-53. doi: 10.1046/j.1432-1327.1998.2550647.x.
Chrysiogenes arsenatis is the only bacterium known that respires anaerobically using arsenate as the terminal electron acceptor and the respiratory substrate acetate as the electron donor. During growth, the arsenate is reduced to arsenite; the reduction is catalyzed by an arsenate reductase. This study describes the purification and characterization of a respiratory arsenate reductase (Arr). The enzyme consists of two subunits with molecular masses of 87 kDa (ArrA) and 29 kDa (ArrB), and is a heterodimer alpha1beta1 with a native molecular mass of 123 kDa. The arsenate reductase contains molybdenum, iron, acid-labile sulfur and zinc as cofactor constituents. The Km of the enzyme for arsenate is 0.3 mM and the Vmax is 7013 micromol arsenate reduced x min(-1) x mg protein(-1). Nitrate, sulfate, selenate and fumarate cannot serve as alternative electron acceptors for the arsenate reductase. Synthesis of the protein is regulated, as arsenate must be present during growth for the enzyme to be fully induced. The N-terminus of ArrA is similar to a number of procaryotic molybdenum-containing polypeptides (e.g. the formate dehydrogenases H and N of Escherichia coli). The N-terminus of ArrB is similar to iron-sulfur proteins. The respiratory arsenate reductase of C. arsenatis is different from the non-respiratory arsenate reductases of E. coli and Staphylococcus aureus.
砷酸产金色菌是已知的唯一一种以砷酸盐作为末端电子受体、以呼吸底物乙酸盐作为电子供体进行厌氧呼吸的细菌。在生长过程中，砷酸盐被还原为亚砷酸盐；这种还原反应由一种砷酸还原酶催化。本研究描述了一种呼吸型砷酸还原酶（Arr）的纯化及特性。该酶由两个亚基组成，分子量分别为87 kDa（ArrA）和29 kDa（ArrB），是一种天然分子量为123 kDa的异源二聚体α1β1。砷酸还原酶含有钼、铁、酸不稳定硫和锌作为辅因子成分。该酶对砷酸盐的Km值为0.3 mM，Vmax为7013 μmol砷酸盐还原·分钟⁻¹·毫克蛋白⁻¹。硝酸盐、硫酸盐、硒酸盐和富马酸盐不能作为砷酸还原酶的替代电子受体。蛋白质的合成受到调控，因为在生长过程中必须存在砷酸盐才能使该酶完全被诱导。ArrA的N末端与许多原核含钼多肽（如大肠杆菌的甲酸脱氢酶H和N）相似。ArrB的N末端与铁硫蛋白相似。砷酸产金色菌的呼吸型砷酸还原酶与大肠杆菌和金黄色葡萄球菌的非呼吸型砷酸还原酶不同。
