Thermally induced transitions can be measured by calorimetric techniques in a variety of biological samples. Examples of these transitions include protein denaturation, double strand to single strand transitions in nucleic acids, and gel to liquid crystalline transitions in membranes and lipid bilayers. High precision differential scanning calorimetry provides the most complete thermodynamic description of these systems. There are however many uncertainties regarding the kinetics of these same thermally induced transitions, due in part to the many different techniques that have been employed in these kinetics studies. This research is a pilot project designed to develop, test and apply a new research technique in this area of molecular biophysics. The research proposed is to test the feasibility of applying dynamic response measurement techniques in a high precision microcalorimeter to measure the kinetics of thermally induced transitions. These techniques are presently available by means of a computer controlled differential scanning calorimeter designed and assembled in the author's laboratory. Power sine waves inside the measured sample yielding temperature amplitudes from less than 0.0001 degrees C to greater than 0.2 degrees C can be measured in the frequency range from 1 Hz to beyond 0.0001 Hz. A substantial degree of uncertainty in the reported kinetic studies lie within this measurable range. When a sample is in place which absorbs energy it will distort the temperature cycles in the region where the frequencies of the power input and the molecular transition kinetics overlap. These dynamic response techniques will be applied to study the kinetics of transitions in phospholipid bilayers with and without cholesterol, and folding transitions in globular proteins. Reliable kinetics information is vital in these biological systems since any proposed molecular mechanisms of function in proteins and membranes must be consistent with experimentally verifiable data. The long term goal of this proposed research is the successful development of a new research technique for obtaining molecular relaxation kinetics by measuring thermal energy absorption as a function of frequency.
