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Cooperative cyanide dissociation from ferrous hemoglobin.
M Brunori1, G Antonini, M Castagnola
1Dipartimento di Scienze Biochimiche, Università La Sapienza, Roma, Italy.
The Journal of Biological Chemistry
|February 5, 1992
Summary
Cyanide dissociation from ferrous hemoglobin is influenced by its quaternary structure. Allosteric effectors stabilize the T state, increasing dissociation rates and revealing new insights into hemoglobin function.
Area of Science:
- Biochemistry
- Molecular Biology
- Spectroscopy
Background:
- Cyanomethemoglobin (Hb+CN-) reduction forms an intermediate cyanide derivative of ferrous hemoglobin.
- This intermediate rapidly dissociates due to low ligand affinity for heme iron.
Purpose of the Study:
- To investigate the properties of the intermediate species formed during cyanomethemoglobin reduction.
- To elucidate the kinetics and spectroscopic characteristics of cyanide dissociation from hemoglobin and its subunits.
Main Methods:
- Transient spectroscopy was employed to study human hemoglobin and its isolated alpha and beta chains.
- Dithionite was used for reduction, with methyl viologen added to resolve overlapping reaction time courses.
- Spectroscopic and kinetic analyses were performed in the presence and absence of carbon monoxide (CO).
Main Results:
- Cyanide dissociation from isolated alpha and beta chains is a simple process with similar rate parameters but spectroscopic inequivalence.
- Cooperative effects significantly control cyanide dissociation rates from hemoglobin, analogous to oxygen binding.
- Allosteric effectors, such as inositol hexaphosphate, accelerate cyanide dissociation by stabilizing the T state.
Conclusions:
- The quaternary state of hemoglobin controls the rate of cyanide dissociation.
- This study provides novel insights into hemoglobin structure-function relationships by analyzing cyanide as an additional ligand.
- The findings highlight the role of allosteric regulation in modulating ligand dynamics in hemoglobin.