Fig. 3.

Mg²⁺ and Fe²⁺ stimulate translational activity over a range of concentrations. The activity of the translation product (DHFR, which catalyzes the oxidation of NADPH, with a maximum absorbance at 340 nm) was used as a proxy for protein production. Translation reactions were run for 120 min. All translation reactions contained 2.5 mM background Mg²⁺, to which varying amounts of additional Mg²⁺ or Fe²⁺ were added. The error bars for triplicate experiments (n = 3) are plotted as the SEM. The Inset shows the absorbance spectrum and chemical structures of the substrate, NADPH, and product, NADP⁺. The dashed circles highlight the nitrogen and carbon atoms of dihydrofolic acid that are reduced by DHFR using NADPH.