Ionic strength effects in the aminoacylation of valine transfer ribonucleic acid.

It has been shown that the enzymic addition of valine to valine transfer ribonucleic acid (tRNA) of Escherichia co2i is exceedingly sensitive to alcohol or salt concentrations and that the rate of the reaction is predictable from the Debye-Htickel equations, if it is assumed that there are somewhat more than 4 positive charges and 4 negative charges involved in the rate-determining step. (For instance, the binding of the tRNA to the ligase and the rate of the subsequent reaction may be increased J-fold by 10% ethanol or decreased 6-fold by 0.15 M NaCl.) The reaction has been found to be base-catalyzed, tris(hydroxymethyl)aminomethane, imidazole, and NH4+ being stimulator-y at low concentrations but following the salt inhibition curve at concentrations above 0.1 M. It is noted that other enzymic reactions involving RNA show a strong salt or solvent dependence of the same magnitude and kind. It is concluded that, although van der Waals’ forces, hydrogen bonds, and hydrophobic bonds may determine specificity, the binding of an RNA molecule to an enzyme also requires a great deal of ionic bonding.