title: Cold denaturation of myoglobin.
abstract: The stability of the structure of sperm whale metmyoglobin has been studied in various solutions, in the temperature range -8 degrees C to 100 degrees C, by scanning microcalorimetry, light absorption, circular dichroism, nuclear magnetic resonance spectroscopy and viscosimetry. It has been shown that in 10 mM-sodium acetate solutions (pH 3.5 to 3.9) the protein molecule undergoes a reversible conformational transition into a non-compact disordered state not only when the solution is heated above room temperature but also when it is cooled. In this state the protein does not have a tertiary structure, although it retains some residual ellipticity, which may be caused by the fluctuating alpha-helical conformation of the unfolded polypeptide chain. The disruption of the native protein structure both on cooling (cold-denaturation) and on heating (heat-denaturation) proceeds in an "all-or-none" manner, with a significant and similar increase of the protein heat capacity, but with inverse enthalpic and entropic effects: the enthalpy and entropy of the protein molecule decrease during cold-denaturation and increase during heat-denaturation.
mesh_terms: D000818:Animals; D002151:Calorimetry; D002591:Cetacea; D003080:Cold Temperature; D006420:Hemeproteins; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D008786:Metmyoglobin; D011489:Protein Denaturation; D013057:Spectrum Analysis; D013696:Temperature; D013816:Thermodynamics; D014907:Whales
chemical_list: D006420:Hemeproteins; D008786:Metmyoglobin