Effect of Ambient Conditions on Conformations of Tryptophan Transfer Ribonucleic Acid of Escherichia coli

Abstract

Abstract The interconversion of two conformations of tryptophan transfer RNA of Escherichia coli, Form I (native form) and Form II (denatured form), is a reversible, first order reaction. The two forms are metastable at low temperatures, and their interconversion is accelerated by increasing temperature. The free energy change of denaturation decreases with decreasing cation concentration and increasing temperature. Changes of enthalpy and entropy of denaturation and activation for both denaturation and renaturation are positive, indicating that breakage and formation of hydrogen-bonded base pairs and changes in base stacking are probably involved in the process of interconversion. High concentrations of monovalent cations favor Form I. On the other hand, low concentrations of monovalent cations favor Form II and competitively inhibit the production of Form I by divalent cations. The tryptophan tRNA in acidic buffer (pH 3.5 to 4.0) or in water is converted instantly to Form I when added to the acylation mixture. At equilibrium, the fractional amounts of Form I and Form II are independent of the tRNA concentration.