Biochemical and thermodynamic characteristics of myoglobin from the skeletal muscle of sei whale Balaenoptera borealis

Myoglobin (Mb) was purified from the skeletal muscle of a sei whale Balaenoptera borealis through a combination of ammonium sulfate fractionation and a series of column chromatography. The absorption maxima of the oxidized form appeared at 543 and 581 nm, while that of the met form appeared at 638 nm. The autooxidation rate at 25°C and pH 7.0 was calculated to be 0.04 h ^-1. The thermostability of this Mb at pH 7.0 as observed in the temperature dependency of circular dichroism (CD) showed that the apparent free energy of folding is -12.6 kJ/mol and the apparent melting temperature is 64.1°C. The a-helical content at 5°C and 80°C was 75.4% and 30.9%, respectively. Differential scanning microcalorimetry (DSC) showed that a large structural change took place at 81.8°C. CD measurement and DSC analysis gave considerable differences in the thermal denaturation profiles of this Mb, suggesting that the helices and hydrophobic interaction collapse in different temperature ranges. Finally, structural characteristics of this Mb were discussed based on the modeled tertiary structure.