Document Detail

Cooperative mechanism in the homodimeric myoglobin from Nassa mutabilis.
MedLine Citation:
PMID:  9485438     Owner:  NLM     Status:  MEDLINE    
Oxygen binding and spectroscopic properties of the homodimeric myoglobin (Mb) from the prosobranchia sea snail Nassa mutabilis have been investigated. Oxygen equilibrium curves are pH-independent and cooperative with P50 = 5 +/- 1 mmHg and n approximately 1.5. Circular dichroism spectra of the oxygenated and deoxygenated form of N. mutabilis Mb are superimposable between 190 and 250 nm, suggesting a mechanism for cooperative ligand binding that does not involve changes in the alpha-helical content of the whole protein. The oxygen dissociation process is biphasic and pH-dependent, with different pKa values (=6.7 +/- 0.2 and 8.5 +/- 0.3) for the two phases. Moreover, the activation energy is essentially the same for both oxygen dissociation processes (Ea = 56.4 +/- 2.1 kJ/mol for the fast phase, and Ea = 53.8 +/- 1.9 kJ/mol for the slow phase), indicating that the rate difference for O2 dissociation between the diliganded and the monoliganded species is mostly dependent on a variation of the activation entropy. Ferrous nitrosylated N. mutabilis Mb shows, at alkaline and neutral pH, axial and rhombic X-band EPR signals, respectively, which display below pH 6 a three-hyperfine pattern typical of five-coordination. The results presented here suggest that in N.mutabilis Mb the kinetic control of cooperativity operates through a mechanism never observed before in other hemoproteins, which requires a ligand-linked large enhancement for the value of the oxygen association process in a molecule not undergoing changes in quaternary structure.
M Coletta; P Ascenzi; F Polizio; G Smulevich; R del Gaudio; M Piscopo; G Geraci
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Biochemistry     Volume:  37     ISSN:  0006-2960     ISO Abbreviation:  Biochemistry     Publication Date:  1998 Mar 
Date Detail:
Created Date:  1998-04-03     Completed Date:  1998-04-03     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  0370623     Medline TA:  Biochemistry     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  2873-8     Citation Subset:  IM    
Department of Experimental Medicine and Biochemical Sciences, University of Roma Tor Vergata, Via di Tor Vergata 135, 00133 Roma, Italy.
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MeSH Terms
Circular Dichroism
Hemoglobins / chemistry
Myoglobin / chemistry*,  metabolism
Oxygen / metabolism
Protein Binding
Protein Conformation
Reg. No./Substance:
0/Hemoglobins; 0/Ligands; 0/Myoglobin; 151087-63-7/dimeric hemoglobin, Scapharca inaequivalvis; 7782-44-7/Oxygen

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