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A simplified method for titrations of biochemical systems is described as well as extensive error propagation through the data analysis. This work uses a Tronac Model 450 isoperibol titration calorimeter. Sample volumes of 2 ml are used and total heats of less than 5 mcal can be routinely measured. The binding of 3'-CMP to bovine pancreatic ribonuclease A is used to illustrate the methods. The binding enthalpy can be determined with a standard deviation of 1.5% and the free energy with a standard deviation of 2 to 3%.

Two improved systems for the determination of the difference in pH between two solutions at the same temperature are described, both of which have a long-term stability of ±1 × 10 −4 pH unit and a peak-to-peak noise level of 5 × 10 −5 pH unit when operated in the differential mode. The cells are constructed of Delrin which has been found to be inert in biological fluids. These cells, with a volume of 1 ml, can be electrically connected to each other via a dialysis membrane and are thermostated during the duration of the pH measurements to ±0.01°C. In a second configuration, combination microelectrodes are inserted into each cell; thus the dialysis membrane is not necessary. To demonstrate the application of these systems to reactions of biological interest where pH changes occur, we investigated the hexokinase-catalyzed reaction between ATP and glucose in a phosphate buffer. The concentrations of glucose determined from the observed changes in pH by a numerical solution to the equilibrium equations are in excellent agreement with the analytical values.