Franchi Marco, Ferris James P, Gallori Enzo
Department of Animal Biology and Genetics, University of Florence, Italy.
Orig Life Evol Biosph. 2003 Feb;33(1):1-16. doi: 10.1023/a:1023982008714.
Monovalent ([Na+] > 10 mM) and divalent ([Ca2+], [Mg2+] > 1.0 mM) cations induced the precipitation of nucleic acid molecules. In the presence of clay minerals (montmorillonite and kaolinite), there was adsorption instead of precipitation. The cation concentration needed for adsorption depended on both the valence of the cations and the chemical nature of the nucleic acid molecules. Double-stranded nucleic acids needed higher cation concentrations than single-stranded ones to be adsorbed to the same extent on clay. Divalent cations were more efficient than monovalent ones in mediating adsorption. Adsorption to the clay occurred only when both nucleic acids and cations were present. However, once the complexes were formed, the cations could not be removed from the system by washing, indicating that they are directly involved in the association between nucleic acids and mineral surfaces. These observations indicate that cations take part directly in the formation of nucleic acid-clay complexes, acting as a 'bridge' between the negative charges on the mineral surface and those of the phosphate groups of the genetic polymer. The relatively low cation concentrations needed for adsorption and the ubiquitous presence of clay minerals in the environment suggest that the adsorption of nucleic acids on mineral surfaces could have taken place in prebiotic habitats. This may have played an important role in the formation and preservation of nucleic acids and/or their precursor polymers.
单价阳离子（[Na+]>10 mM）和二价阳离子（[Ca2+]、[Mg2+]>1.0 mM）会诱导核酸分子沉淀。在存在粘土矿物（蒙脱石和高岭土）的情况下，发生的是吸附而非沉淀。吸附所需的阳离子浓度取决于阳离子的价态和核酸分子的化学性质。双链核酸比单链核酸需要更高的阳离子浓度才能在粘土上达到相同程度的吸附。二价阳离子在介导吸附方面比单价阳离子更有效。只有当核酸和阳离子都存在时才会发生对粘土的吸附。然而，一旦形成复合物，通过洗涤无法将阳离子从系统中去除，这表明它们直接参与了核酸与矿物表面之间的结合。这些观察结果表明，阳离子直接参与核酸 - 粘土复合物的形成，充当矿物表面负电荷与遗传聚合物磷酸基团负电荷之间的“桥梁”。吸附所需的相对较低的阳离子浓度以及环境中粘土矿物的普遍存在表明，核酸在矿物表面的吸附可能在益生元栖息地就已发生。这可能在核酸和/或其前体聚合物的形成和保存中发挥了重要作用。
