DEVELOPMENT OF BIOCALORIMETERS FOR SOLUTION AND CELL BIOCHEMICAL STUDIES

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An all tantalum stopped-flow microcalorimeter, previously reported (Biophysical Journal 49(1986) p.87a; 51(1987) p.443a), has now been used extensively to study the binding enthalpies of DNA-drug interactions. Decomposition of the measured thermograms yields reconstructed thermograms with a time constant of approximately three seconds. Two schemes have been used to reconstruct the measured thermograms. The finite element method of Davids and Berger (J. Biochem & Biophys Methods. 6(1982) p.205-217) requires a knowledge of the physical construction of the calorimeter. The iterative method adapted by Schuette and Mudd (J. Biochem & Biophys Methods, 14 (1987) p. 167-175) requires only that the impulse response be known and digitized at the same rate as the measured thermogram. Results employing both deconvolution methods will be presented. The microcalorimeter is capable of measuring binding enthalpies of 30 microjoules with a standard deviation of 3 microjoules. A reaction requires 80 microliters of each reagent and is completed within 200 seconds thus allowing a typical throughput of 120-150 runs per day. The high resolution of this instrument has permitted accurate measurement of reaction heats at extremely dilute reagent concentrations thereby precluding the need to correct the binding enthalpies for drug and/or DNA aggregation.