Alteration of the proximal bond energy in the unliganded form of the homodimeric myoglobin from Nassa mutabilis Kinetic and spectroscopic evidence

FEBS Letters

Mantini, Anna Rita⁴  Ascenzi, Paolo²  Gaudio, Rosanna Del¹  Coletta, Massimo⁵  Smulevich, Giulietta⁴  Piscopo, Marina³  Geraci, Giuseppe³ 

[1] CNR Institute of Protein Biochemistry and Enzymology, Via Guglielmo Marconi 10, 80077 Arco Felice (NA), Italy;Department of Pharmaceutical Chemistry and Technology, University of Turin, Via Pietro Giuria 9, 10125 Turin, Italy;Department of Genetics, General and Molecular Biology, University of Naples, Via Mezzocannone 8, 80134 Naples, Italy;Department of Chemistry, University of Florence, Via Gino Capponi 9, 50121 Florence, Italy;Department of Molecular, Cellular and Animal Biology, University of Camerino, Via Filippo Camerini 2, 62032 Camerino (MC), Italy

关键词: Myoglobin;    Nassa mutabilis homodimeric Mb;    CO binding kinetics;    Resonance Raman spectroscopic property;    pH effect;    Mb;    Myoglobin;    Hb;    Hemoglobin;    N. mutabilis Mb;    Nassa mutabilis homodimeric myoglobin;    S. inaequivalvis Hb;    Scapharca inaequivalvis homodimeric hemoglobin;   

DOI  :  10.1016/0014-5793(92)80375-Q

学科分类：生物化学/生物物理

来源: John Wiley & Sons Ltd.

【 摘 要 】

CO binding kinetics to the homodimeric myoglobin (Mb) from Nassa mutabilis has been investigated between pH 1.9 and 7.O. Protonation of the proximal imidazole at low pH (≤ 3.0) and the consequent cleavage of the HisF8NE2-Fe proximal bond brings about a ≈ 20-fold increase of the second-order rate constant for CO binding. This process displays a pK _a = 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 from that operative in other hemoproteins.

【 授权许可】

Unknown