INFLUENCE OF DYNAMIC POWER COMPENSATION IN AN ISOTHERMAL TITRATION MICROCALORIMETER

A theoretical analysis in Laplace's transformed domain based on a powe r balance represents a suitable model for an isothermal titration calo rimeter with dynamic power compensation, designed and implemented in o ur laboratory. A rigorous calibration of the injection system and the calorimetric response was also made. Using electrically generated heat pulses, two different time constants have been determined from the ca lorimetric transfer function and assigned to the physical parts of the calorimeter. The same was done for a protein-ligand interaction. The binding of 2'-CMP to ribonuclease A at low and high ionic strengths wa s used to check the apparatus and the results were compared with those obtained by other authors (Wiseman, T.; Williston, S.; Brandts, J. F. ; Lung-Nan, L. Anal. Biochem, 1989, 179, 131-137), In this case, the a nalysis showed a different time constant for the heat source. Independ ently of the nature of the heat source, the calorimetric time constant s obtained while working under compensation are always smaller than th ose corresponding to a noncompensated system. The improvement of the c alorimetric response introduced by dynamic power compensation is thus explained in terms of the reduction of the time constants characterist ic of the calorimeter. This theoretical model can be used to predict t he shape of the thermogram for any given reaction of either known or s upposed thermodynamic parameters. Therefore, the calorimetric study is extended to the other nucleotides, 2'-UMP and 5'-dUMP, which have not hitherto been reported in the literature.