The 'pH optimum anomaly' of intracellular enzymes of Ferroplasma acidiphilum
The 'pH optimum anomaly' of intracellular enzymes of Ferroplasma acidiphilum
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DOI：
10.1111/j.1462-2920.2005.00907.x
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发表时间：
2006-03-01
影响因子：
5.1
通讯作者：
Ferrer, M
中科院分区：
文献类型：
--
作者：
Golyshina, OV;Golyshin, PN;Ferrer, M
广泛的微生物，即所谓的嗜酸菌，生活在酸性环境中，在pH值为0到3之间生长最好。然而，这些微生物的胞内pH接近中性或略呈酸性。可以预期，专用于胞外功能的酶活性将适应普遍存在的低pH环境(0-3)，而胞内酶将在细胞质的近中性pH(4.6-7.0)时具有最佳活性。酸性铁浆菌是一种细胞壁缺乏的嗜酸古生子，生长最适pH为1.7，其胞内或细胞结合酶的1个羧酸酯酶和3个α-葡萄糖苷酶的基因被克隆并在大肠杆菌中表达，并对其产物进行纯化和鉴定。铁质α-葡萄糖苷酶与已知的糖基水解酶没有序列相似性。所有酶在体外pH值在1.7-4.0范围内均能发挥作用且稳定，最适pH值远低于胞内平均pH值5.6。这一“pH最佳异常”表明，存在尚未被检测到的细胞区划，为我们所分析的酶提供了细胞质pH斑块和低pH环境。
A wide range of microorganisms, the so-called acidophiles, inhabit acidic environments and grow optimally at pH values between 0 and 3. The intracellular pH of these organisms is, however, close to neutrality or slightly acidic. It is to be expected that enzymatic activities dedicated to extracellular functions would be adapted to the prevailing low pH of the environment (0-3), whereas intracellular enzymes would be optimally active at the near-neutral pH of the cytoplasm (4.6-7.0). The genes of several intracellular or cell-bound enzymes, a carboxylesterase and three alpha-glucosidases, from Ferroplasma acidiphilum, a cell wall-lacking acidophilic archaeon with a growth optimum at pH 1.7, were cloned and expressed in Escherichia coli, and their products purified and characterized. The Ferroplasma alpha-glucosidases exhibited no sequence similarity to known glycosyl hydrolases. All enzymes functioned and were stable in vitro in the pH range 1.7-4.0, and had pH optima much lower than the mean intracellular pH of 5.6. This 'pH optimum anomaly' suggests the existence of yet-undetected cellular compartmentalization providing cytoplasmic pH patchiness and low pH environments for the enzymes we have analysed.