Coletta M, Ascenzi P, Smulevich G, Mantini A R, Del Gaudio R, Piscopo M, Geraci G
Department of Molecular, Cellular and Animal Biology, University of Camerino, Italy.
FEBS Lett. 1992 Jan 20;296(2):184-6. doi: 10.1016/0014-5793(92)80375-q.
CO binding kinetics to the homodimeric myoglobin (Mb) from Nassa mutabilis has been investigated between pH 1.9 and 7.0. Protonation of the proximal imidazole at low pH (less than or equal to 3.0) and the consequent cleavage of the HisF8NE2-Fe proximal bond brings about a approximately 20-fold increase of the second-order rate constant for CO binding. This process displays a pKa = 4.0 +/- 0.2, significantly higher than that observed in all other deoxygenated hemoproteins investigated up to now. Such a feature underlies a decreased energy for the HisF8NE2-Fe proximal bond in the unliganded form and it also appears supported by resonance Raman spectroscopy in the low frequency region of the Fe(II) deoxygenated hemoprotein. Further, the pH-rate profile of N. mutabilis Mb, like that of the homodimeric hemoglobin (Hb) from Scapharca inaequivalvis (Coletta, M., Boffi, A., Ascenzi, P., Brunori, M. and Chiancone, E. (1990) J. Biol. Chem. 265, 4828-4830), can be described only by assuming a concerted proton-linked transition with n = 1.8 +/- 0.1. Such a characteristic suggests, also on the basis of the amino acid sequence homology between N. mutabilis Mb and S. inaequivalvis Hb in the region forming the subunit interface, that the interaction mechanism is similar for the two homodimeric proteins, and drastically different Hb in the region forming the subunit interface, that the interaction mechanism is similar for the two homodimeric proteins, and drastically different from that operative in other hemoproteins.
已对pH值在1.9至7.0之间时，多变织纹螺同源二聚体肌红蛋白（Mb）与一氧化碳（CO）的结合动力学进行了研究。在低pH值（小于或等于3.0）下，近端咪唑发生质子化，随后HisF8NE2 - Fe近端键断裂，导致CO结合的二级速率常数增加约20倍。此过程的pKa = 4.0±0.2，显著高于迄今所研究的所有其他脱氧血红蛋白中的观测值。这样的特征表明未结合配体形式下HisF8NE2 - Fe近端键的能量降低，并且在Fe(II)脱氧血红蛋白的低频区域的共振拉曼光谱也支持这一点。此外，多变织纹螺肌红蛋白的pH - 速率曲线，与不等壳毛蚶同源二聚体血红蛋白（Hb）（Coletta, M., Boffi, A., Ascenzi, P., Brunori, M.和Chiancone, E. (1990) J. Biol. Chem. 265, 4828 - 4830）的pH - 速率曲线一样，只有假设n = 1.8±0.1的协同质子偶联转变才能描述。基于多变织纹螺肌红蛋白和不等壳毛蚶血红蛋白在形成亚基界面区域的氨基酸序列同源性，这一特征还表明这两种同源二聚体蛋白质的相互作用机制相似，且与其他血红蛋白中的作用机制截然不同。
