Differential scanning calorimetry study of local anesthetic effects on F1ATPase and submitochondrial particles

The differential scanning calorimetry trace of F1ATPase, prepared from beef heart submitochondrial particles, has a single sharp endothermic transition at 80.5 +/- 1.0 degrees C and a half-height peak width of 2.0 +/- 0.2 degrees. The transition enthalpy is 19 +/- 2 cal/g of protein. Submitochondrial particles (SMP) have a similar peak at 75.1 +/- 0.5 degrees C with a half-height peak width of 1.8 +/- 0.1 degrees and an enthalpy of 5 +/- 1 cal/g of SMP protein. The SMP transition is provisionally identified as being due to membrane-bound F1ATPase. 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 degrees C for F1ATPase and SMP, respectively, and 1.0 mM tetracaine gives peaks at 70.0 and 60.5 degrees C for F1ATPase and SMP, respectively. These anesthetic concentrations also give appreciable inhibition of enzyme activity at 25 degrees C. We conclude that the local anesthetics induce conformational alterations in the F1ATPase-protein complex which result both in enzyme inhibition and in the lowering of the thermal denaturation transition temperature.