Calorimetric Investigations on Thermal Stability of tRNAIle (Yeast) and tRNASer (Yeast)

Abstract
Variation with temperature of the partial heat capacities of tRNAIle ([baker''s] yeast) and tRNASer (yeast) was determined in 2 buffers at various salt conditions by scanning microcalorimetry. The overall molar transition enthalpy, .DELTA.Ht = 320 .+-. 20 kcal mol-1 (1339 .+-. 84 kJ mol-1), is identical for the 2 tRNA species within the limits of experimental error. .DELTA.Ht does not show any dependence on the nature of the buffer, nor does it vary on addition of 1 mM MgCl2 or 150 mM NaCl. Thermal unfolding of the native structure to the random coil cannot adequately be described by a 2-state, concerted transition under the experimental conditions applied in this study, but exhibits a multistep mechanism characterized by sequential unfolding of separable cooperative domains.