Modulation nanocalorimeter in research of thermal denaturation of proteins

The experimental model of the modulation nanocalorimeter has been developed. This nanocalorimeter has the following characteristics : the sensitivity is 50 nW; the base line stability for 3-5 hours is 50 nW; the fast-response is 60 s. In diluted protein solutions the precision measurements of heat flow have been performed with a modulated nanocalorimeter in the StepScan-modulation mode. This mode based on sequences of short intervals of heat (cooling) and isothermal intervals in a given temperature interval. Given functional scheme of the modulated nanocalorimeter is supplemented by an experimental estimation of the value of temperature difference along the length of the calorimetric chamber at its heating at a rate of 0.2 K/min. This estimation is made from the melting data of a test temperature sample in the calorimetric chamber. The test temperature sample is 1mg Gallium. It is shown, that the difference between temperatures of the chamber top and bottom does not exceed 0.02 K. Thus, it is experimentally confirmed that calorimetric chambers have equal temperature along the whole length, as the obtained temperature difference is less than the absolute error of a sample temperature measurement with modulated nanocalorimeter. All modern scanning microcalorimeters developed by foreign corporations have a disadvantage in comparison with modulated nanocalorimeter, as they do not provide operation in the modulation mode. Modulated nanocalorimeter is a computer aided instrument. For modulated nanocalorimeter we have developed the software, providing the calorimeter operation and calculation of a complete heat flow, and also kinetic and reversible parts of a complete heat flow, which is confirmed by the experimental data. The research of thermal denaturation of ovalbumin and of lysozyme was carried out. It is shown that the modulation nanocalorimetry gives an opportunity to discriminate qualitatively different mechanisms of thermal denaturation of proteins.