Salerno J C, Bolgiano B, Poole R K, Gennis R B, Ingledew W J
Department of Biochemistry and Microbiology, University of St. Andrews, United Kingdom.
J Biol Chem. 1990 Mar 15;265(8):4364-8.
The cytochrome bo quinol oxidase of Escherichia coli is one of two respiratory O2 reductases which the bacterium synthesizes. The enzyme complex contains copper and 2 mol of b-type heme. Electron paramagnetic resonance (epr) spectroscopy of membranes from a strain having amplified levels of this enzyme complex reveals signals from low- and high-spin b-type hemes, but the copper, now established as a component of the oxidase, is not directly detectable by epr. The high-spin signal from the cytochrome bo complex, which we attribute to cytochrome o, when titrated potentiometrically, gives a bell-shaped curve. The low potential side of this curve is biphasic (Em7 approximately 180 and 280 mV) and corresponds to the reduction/oxidation of the cytochrome(s). The high potential side of the bell-shaped curve is monophasic (Em7 approximately 370 mV) and is proposed to be due to reduction/oxidation of a copper center which, when in the Cu(II) form, is tightly spin-coupled to a heme, probably cytochrome o, resulting in a net even spin system and loss of the epr spectrum. The low-spin cytochrome b titrates biphasically with Em7 values of approximately 180 and 280 mV, similar to the high-spin component but without the loss of signal at high potentials.
大肠杆菌的细胞色素bo泛醌氧化酶是该细菌合成的两种呼吸性O2还原酶之一。该酶复合物含有铜和2摩尔的b型血红素。对具有该酶复合物高水平表达的菌株的膜进行电子顺磁共振（epr）光谱分析，可揭示低自旋和高自旋b型血红素的信号，但现已确定为氧化酶组分的铜不能通过epr直接检测到。细胞色素bo复合物的高自旋信号（我们将其归因于细胞色素o）在进行电位滴定法时，会给出一条钟形曲线。该曲线的低电位侧是双相的（Em7约为180和280 mV），对应于细胞色素的还原/氧化。钟形曲线的高电位侧是单相的（Em7约为370 mV），据推测是由于一个铜中心的还原/氧化所致，该铜中心在Cu(II)形式时与一个血红素紧密自旋偶联，可能是细胞色素o，导致净偶数自旋系统并使epr光谱消失。低自旋细胞色素b以双相方式滴定，Em7值约为180和280 mV，与高自旋组分相似，但在高电位时没有信号损失。
