Kitahara Y, Matsuoka A, Kobayashi N, Shikama K
Biological Institute, Faculty of Science, Tohoku University, Sendai, Japan.
Biochim Biophys Acta. 1990 Mar 29;1038(1):23-8. doi: 10.1016/0167-4838(90)90005-z.
Native oxymyoglobin (MbO2) was isolated directly from the skeletal muscle of bigeye tuna (Thunnus obesus) with complete separation from metmyoglobin (metMb) on a CM-cellulose column. It was examined for its stability properties over a wide range of pH values (pH 5-12) in 0.1 M buffer at 25 degrees C. When compared with sperm whale MbO2 as a reference, the tuna MbO2 was found to be much more susceptible to autoxidation. Kinetic analysis has revealed that the rate constant for a nucleophilic displacement of O2- from MbO2 by an entering water molecule is 10-times higher than the corresponding value for sperm whale MbO2. The magnitude of the circular dichroism of bigeye tuna myoglobin at 222 nm was comparable to that of sperm whale myoglobin, but its hydropathy profile revealed the region corresponding to the distal side of the heme iron to be apparently less hydrophobic. The kinetic simulation also demonstrated that accessibility of the solvent water molecule to the heme pocket is clearly a key factor in the stability properties of the bound dioxygen.
天然氧合肌红蛋白（MbO₂）直接从大眼金枪鱼（Thunnus obesus）的骨骼肌中分离得到，并在CM-纤维素柱上与高铁肌红蛋白（metMb）完全分离。在25℃下，于0.1 M缓冲液中，对其在广泛pH值范围（pH 5 - 12）内的稳定性进行了检测。与作为参照的抹香鲸MbO₂相比，发现金枪鱼MbO₂更容易发生自氧化。动力学分析表明，进入的水分子将O₂⁻从MbO₂中亲核取代的速率常数比抹香鲸MbO₂的相应值高10倍。大眼金枪鱼肌红蛋白在222 nm处的圆二色性大小与抹香鲸肌红蛋白相当，但其亲水性图谱显示，对应于血红素铁远端的区域明显疏水性较低。动力学模拟还表明，溶剂水分子进入血红素口袋的难易程度显然是结合双氧稳定性的关键因素。
