Denaturation midpoint
Encyclopedia
Assuming two-state protein folding
, denaturation midpoint is defined as that temperature
(Tm) or denaturant
concentration
(Cm) at which both the folded and unfolded states
are equally populated at equilibrium.
If the widths of the folded and unfolded wells are assumed to be equal both these states will have identical free energies at the midpoint. However, for natural proteins this is not the case. There is an inherent asymmetry as evidenced by the difference in heat capacities
between them - the folded ensemble has a lower heat capacity (in other words, lower fluctuations thus indicating a narrower well) than the unfolded ensemble. This would mean that the free energy of the folded state is lower at the denaturation midpoint than the unfolded state. In such a scenario, the temperature at which both the wells have identical free energies is termed the characteristic temperature (To).
Protein folding
Protein folding is the process by which a protein structure assumes its functional shape or conformation. It is the physical process by which a polypeptide folds into its characteristic and functional three-dimensional structure from random coil....
, denaturation midpoint is defined as that temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
(Tm) or denaturant
Denaturation (biochemistry)
Denaturation is a process in which proteins or nucleic acids lose their tertiary structure and secondary structure by application of some external stress or compound, such as a strong acid or base, a concentrated inorganic salt, an organic solvent , or heat...
concentration
Concentration
In chemistry, concentration is defined as the abundance of a constituent divided by the total volume of a mixture. Four types can be distinguished: mass concentration, molar concentration, number concentration, and volume concentration...
(Cm) at which both the folded and unfolded states
Denaturation (biochemistry)
Denaturation is a process in which proteins or nucleic acids lose their tertiary structure and secondary structure by application of some external stress or compound, such as a strong acid or base, a concentrated inorganic salt, an organic solvent , or heat...
are equally populated at equilibrium.
If the widths of the folded and unfolded wells are assumed to be equal both these states will have identical free energies at the midpoint. However, for natural proteins this is not the case. There is an inherent asymmetry as evidenced by the difference in heat capacities
Heat capacity
Heat capacity , or thermal capacity, is the measurable physical quantity that characterizes the amount of heat required to change a substance's temperature by a given amount...
between them - the folded ensemble has a lower heat capacity (in other words, lower fluctuations thus indicating a narrower well) than the unfolded ensemble. This would mean that the free energy of the folded state is lower at the denaturation midpoint than the unfolded state. In such a scenario, the temperature at which both the wells have identical free energies is termed the characteristic temperature (To).