12 The Role of Metal Ions in RNA Biochemistry

Abstract

Approximately two-thirds of the elements in the periodic table can be categorized as metals. Besides luster, malleability, and conductivity, one of the fundamental characteristics of metals is their low ionization potential. As a result, the ionic forms of these elements predominate in the biosphere. Considering the diverse properties of these ions, it is not surprising that through the process of evolution, metal ions have been co-opted into numerous roles in biology. Metal ions are required for so many biochemical reactions that it is likely that they also had an important role in the RNA world. To understand both modern and prebiotic RNA biochemistry, it is therefore essential to have a basic understanding of these inorganic elements.

Metal ions were abundant in the primordial soup. It is believed that 3.8 × 10⁹ years ago, the ocean was between 80°C and 100°C with a pH possibly as low as 6 (Bengston 1994). Table 1 shows the concentrations of the most common metal ions in today’s seas and in blood plasma. Although the concentrations of most of these ions in the prebiotic ocean are not known, the higher temperature and lower pH relative to the current ocean would have solvated a variety of ions and leached metal ions from the mineral-rich ocean beds. Therefore, the concentrations would have been significantly higher than the current values. One important additional difference is the extremely low concentration of easily oxidized metal ions such as Fe(II). Ferrous ion has been predicted to have been very abundant in...