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Origin of the roles of potassium in biology
BioEssays ( IF 3.2 ) Pub Date : 2020-12-06 , DOI: 10.1002/bies.202000302
John A Raven 1, 2, 3
Affiliation  

Korolev[1] points out the high potassium:sodium ratio in cells despite the almost universal[2] higher concentration of sodium than potassium in the environment of cells, and bases the requirement for potassium movement into the cytosol of bacteria on the chemiosmotic mechanism of energy transduction. Here oxidation‐reduction reactions in the plasma membrane pump protons from the cytosol into the external medium, generating a proton electrochemical potential difference or proton motive force (PMF) comprised of an electrical potential difference (inside negative) and a pH difference (inside alkaline). Downhill proton influx through the ATP synthase converts ADP and inorganic phosphate into ATP and completes the proton cycle. A slightly smaller influx than efflux of protons means a pH increase in the cytosol; this pH increase is small as a result of the pH buffer capacity of the cytosol.[1] The net efflux of the positively charged protons also means that the inside negative electrical potential difference across the plasma membrane increases according to the capacitance of the plasma membrane, and rapidly becomes so large that the membrane undergoes dielectric breakdown.[1] This can be avoided by the voltage‐driven influx of a cation or efflux of an anion. Korolev[1] shows that potassium influx was favored in evolution for this role, as a result of relatively low concentration meaning that avoiding hyperpolarization does not lead to large increases in intracellular concentrations of solutes, and because potassium‐selective channels can evolve amplifying small potassium‐selectivity of fixed negative changes by having a number of them in series in the channel

The early evolution of chemiosmotic energy coupling is a feature of some models of the origin of life, e.g. in marine hydrothermal vents,[1] and also for the last universal common ancestor (LUCA) of present‐day organisms.[3] While the model[1] using enzymes and transporters that molecular phylogeny shows to be ancient has sodium as the cycling ion in the chemiosmotic ATP production, there is the same requirement for a means of offsetting very large inside‐negative electrical potentials as for proton‐coupled ATP generation.[1] Work on ion‐pumping rhodopsins shows a relatively facile evolutionary interconversion among protons, sodium and chloride as the actively transported ion.[3, 4]

Korolev[1] focused on high osmolarity cellular environments, cells in seawater and in metazoans; the same principles apply to organisms in freshwater bacteria, e.g. the cyanobacterium Gloeobacter, with photosynthetic, respiratory and proton‐pumping rhodopsin‐based chemiosmotic coupling at the plasma membrane.[5] These principles also apply to regulating the PMF in chemiosmotic coupling at the plasma membrane of[5] intracellular membranes such as the membrane separating the thylakoid lumen from the cytosol of cyanobacteria other than Gloeobacter, and the chloroplast stroma of eukaryotic oxygenic photosynthetic organisms. Here the acidic and electropositive compartment is the thylakoid lumen, and potassium channels, and also chloride channels, regulate the components of the PMF, with important implications for other photosynthetic processes.[5]



中文翻译:

钾在生物学中作用的起源

Korolev [ 1 ]指出尽管普遍存在[ 2 ],但细胞中钾钠比例高细胞环境中钠的浓度比钾的浓度高,并且钾对进入细菌胞质溶胶的需求基于能量转换的化学渗透机制。质膜中的氧化还原反应将质子从细胞质中泵入外部介质,产生质子电化学势差或质子动力(PMF),由电势差(负值)和pH值差(碱性值)组成。通过ATP合酶的下坡质子流入将ADP和无机磷酸盐转化为ATP,并完成了质子循环。流入量小于质子流出量意味着细胞质中的pH值增加;由于细胞溶质的pH缓冲能力,pH的增加很小。[ 1 ]带正电的质子的净流出还意味着,穿过质膜的内部负电势差根据质膜的电容而增加,并且迅速变大以至于该膜遭受介电击穿。[ 1 ]可以通过电压驱动的阳离子流入或阴离子的流出来避免这种情况。科罗廖夫[ 1 ]表明钾流入量在该作用中受进化的青睐,这是因为相对较低的浓度意味着避免超极化不会导致溶质的细胞内浓度大幅增加,并且因为钾选择性通道可以进化,从而扩大了固定钾的小选择性。在频道中串联多个负面变化

化学渗透能耦合的早期演化是某些生命起源模型的特征,例如在海洋热液喷口中,[ 1 ]以及现代生物的最后通用祖先(LUCA)。[ 3 ]尽管模型[ 1 ]使用的分子和系统发育已被证明是古老的酶和转运蛋白,在化学渗透ATP的产生中具有钠作为循环离子,但是对于抵消非常大的内部负电势的方法的要求与用于质子偶联的ATP生成。[ 1 ]离子泵视紫红质的研究表明,质子,钠和氯化物之间的相互作用相对较容易,这是活性离子。[ 3,4 ]

Korolev [ 1 ]专注于高渗透压细胞环境,海水和后生动物中的细胞;相同的原理也适用于淡水细菌中的生物,例如蓝细菌Gloeobacter,其质膜上具有基于光合,呼吸和质子泵视紫红质的化学渗透耦合。[ 5 ]这些原则也适用于在质膜调节化学渗透耦合PMF [ 5 ]细胞内膜如膜从蓝藻以外的胞质溶胶中分离类囊体腔Gloeobacter,以及真核含氧光合生物的叶绿体基质。酸性和正电区室是类囊体腔,钾通道以及氯通道调节PMF的成分,对其他光合作用过程具有重要意义。[ 5 ]

更新日期:2020-12-22
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