Differential scanning calorimetry study of local anesthetic effects on F sub(1)ATPase and submitochondrial particles particles

The differntial scanning calorimetry trace of F sub(1)ATpase, prepared from beef heart submitochondrial particles, has a single sharp endothermic transition at 80.5 plus or minus 1.0 degree C and a half-height peak width of 2.0 plus or minus 0.2 degree . The transition enthalpy is 19 plus or minus 2 cal/g of protein. Submitochondrial particles (SMP) have a similar peak at 75.1 plus or minus 0.5 degree C with a half-height peak width of 1.8 plus or minus 0.1 degree and an enthalpy of 5 plus or minus 1 cal/g of SMP protein. The SMP transition is provisionally identified as being due to membrane-bound F sub(1)ATPase. Tetracaine and dibucaine cause these transitions to shift to lower temperatures; addition of 0.3 mM dibucaine gives peaks at 71.7 and 64.9 degree C for F sub(1)ATpase and SPM, respectively, and 1.0 mM tetracaine gives peaks at 70.0 and 60.5 degree C for F sub(1)ATPase and SMP, respectively. These anesthetic concentrations also give appreciable inhibition of enzyme activity at 25 degree C. The authors conclude that the local anesthetics induce conformational alterations in the F sub(1)ATpase-protein complex which result both in enzyme inhibition and in the lowering of the thermal denaturation transition temperature.