Critical Temperature of Secondary Structural Change of Myoglobin in Thermal Denaturation up to 130 °C and Effect of Sodium Dodecyl Sulfate on the Change

• Published in: The journal of physical chemistry. B Vol. 114; no. 7; pp. 2430 - 2434
• Main Authors: Moriyama, Yoshiko, Takeda, Kunio
• Format: Journal Article
• Language: English
• Published: American Chemical Society 25.02.2010
• Subjects: B: Surfactants, Membranes
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp908700j

The secondary structural change of horse heart myoglobin was examined in the thermal denaturation up to 130 °C. The original helicity of 82% gradually decreased to 67% with rise of temperature until 75 °C. Thereafter, it suddenly decreased to 24% at 90 °C and then slightly decreased to 14% at 130 °C. The helices of this protein were mostly destroyed between 75 and 100 °C. On the other hand, upon cooling to 25 °C from temperatures below 75 °C, the helicity completely recovered to the original value, but it did not after heating to temperatures above 80 °C. Thus, myoglobin maintains the reversibility of the structural change up to a temperature as high as 75 °C. This protein had another critical temperature around 90−100 °C in addition to 75 °C in the present thermal denaturation. Upon cooling to 25 °C after heating to temperatures above 80 °C, the extent of recovered helicity decreased with rise of temperature before cooling. The additive effect of sodium dodecyl sulfate (SDS) on the structural change of myoglobin differed below and above the critical temperature at 75 °C. In the temperature range below 75 °C where the structural change was reversible, the presence of SDS cooperated with the thermal denaturation to disrupt the structure. On the contrary, the presence of the surfactant more or less restrained the decrement of helicity at high temperatures above 85 °C. The helicity decreased and increased with an increase of SDS concentration upon cooling to 25 °C after heating to temperatures below 75 °C and after heating to temperatures above 85 °C, respectively. Then, upon cooling to 25 °C from any temperature, the helicity settled to a magnitude around 60% in the presence of the surfactant above 0.6 mM.