A comparative calorimetric study on tRNA unfolding

The heat effects involved in thermal unfolding of five tRNAs with different primary structures have been determined by direct differential scanning microcalorimetry. The overall molar values of the transition enthalpy (delta Ht) are 1150 kJ/mol for tRNA Lys2 (yeast), 1250 kJ/mol for tRNA Phe (yeast), 1350 kJ/mol for tRNA Val (yeast), 1490 kJ/mol for tRNA Val (E. coli) and 1630 kJ/mol for tRNA Tyr (E. coli). The tRNAs differ in their melting behaviour as can be shown by a comparison of the calorimetric curves. The calorimetrically measured delta Ht values are about 350 kJ/mol higher than the transition enthalpy values for the cloverleaf arrangement, which were estimated using the known parameters for G.C and A.U base pairs.