Kinetic studies of temperature changes and oxygen uptake in a differential calorimeter: the heat of oxidation of NADH and succinate

The design and operating characteristics of a differential calorimeter suitable for use with subcellular, particulate enzyme systems are discussed. The application of the calorimeter to the measurement of the enthalpies of oxidation of NADH and succinate with nonphosphorylating heart muscle particles is described. These measurements show that the calorimeter gives results that are reproducible and in agreement with other calorimetric data. The enthalpy of oxidation of NADH by a nonphosphorylating, submitochondrial preparation was determined to be −61.6 ± 1.3 kcal/mole of NADH; this value is independent of pH in all cases and independent of the buffer used, except for phosphate buffer. The enthalpy of oxidation of succinate was determined to be −36.2 ±1.2 kcal/mole, and was independent of the buffer used.