Proteins that oxidize extracellular substrates in Gram-positive bacteria are poorly understood. Ferrimicrobium acidiphilum is an actinobacterium that respires aerobically on extracellular ferrous ions at pH 1.5. In situ absorbance measurements were conducted on turbid suspensions of intact Fm. acidiphilum using an integrating cavity absorption meter designed for that purpose. Initial velocity kinetic studies monitored the appearance of product ferric ions in the presence of catalytic quantities of cells. Cell-catalyzed iron oxidation obeyed the Michaelis-Menten equation with K_m and V_max values of 71 μM and 0.29 fmol/min/cell, respectively. Limited-turnover kinetic studies were conducted with higher concentrations of cells to detect and monitor changes in the absorbance properties of cellular redox proteins when the cells were exposed to limited quantities of soluble reduced iron. A single a-type cytochrome with reduced absorbance peaks at 448 and 605 nm was the only redox-active chromophore that was visible as the cells respired aerobically on iron. The reduced cytochrome 605 exhibited mathematical and correlational properties that were consistent with the hypothesis that oxidation of the cytochrome constituted the rate-limiting step in the aerobic respiratory process, with a turnover number of 35 ± 2 s⁻¹. Genomic and proteomic analyses showed that Fm. acidiphilum could and did express only two a-type heme copper terminal oxidases. Cytochrome 605 was associated with the terminal oxidase gene that is located between nucleotides 31,090 and 33,039, inclusive, in the annotated circular genome of this bacterium.

中文翻译：

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当嗜酸铁微菌依靠可溶性铁进行有氧呼吸时，细胞色素 605 的氧化是限速步骤。


人们对革兰氏阳性菌中氧化细胞外底物的蛋白质知之甚少。 Ferrimicrobium Acidiphilum是一种放线菌，在 pH 1.5 时依靠细胞外亚铁离子进行有氧呼吸。对完整Fm的混浊悬浮液进行原位吸光度测量。 Acidiphilum使用为此目的设计的积分腔吸收计。初始速度动力学研究监测了在细胞催化量存在的情况下产物铁离子的出现。细胞催化的铁氧化遵循 Michaelis-Menten 方程， K _m和V_最大值分别为 71 μM 和 0.29 fmol/min/cell。使用较高浓度的细胞进行有限周转动力学研究，以检测和监测当细胞暴露于有限量的可溶性还原铁时细胞氧化还原蛋白的吸光度特性的变化。在 448 和 605 nm 处吸收峰降低的单一a型细胞色素是细胞在铁上进行有氧呼吸时可见的唯一氧化还原活性发色团。还原的细胞色素605表现出数学和相关特性，这与细胞色素的氧化构成有氧呼吸过程中的限速步骤的假设一致，周转数为35±2 s ^-1 。基因组和蛋白质组分析表明Fm。 Acidiphilum能够并且确实只表达两种a型血红素铜末端氧化酶。 细胞色素 605 与末端氧化酶基因相关，该基因位于该细菌带注释的环状基因组中的核苷酸 31,090 和 33,039 之间（含 31,090 和 33,039）。