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Dissociation of CO from carboxyhemoglobin
The Journal of Biological Chemistry
|July 25, 1976
Summary
This study quantifies stepwise carbon monoxide (CO) dissociation from hemoglobin, revealing reduced cooperativity in carboxyhemoglobin compared to oxyhemoglobin. Ligand interactions are crucial in determining reaction rates.
Area of Science:
- Biochemistry
- Physical Chemistry
- Chemical Kinetics
Background:
- Hemoglobin (Hb) reversibly binds oxygen, but also carbon monoxide (CO).
- Understanding CO dissociation kinetics is vital for hemoglobin function studies.
- Microperoxidase (MP) facilitates studying hemoglobin reactions.
Purpose of the Study:
- To determine stepwise CO dissociation rate constants for carboxyhemoglobin.
- To investigate the influence of 2,3-diphosphoglyceric acid on CO dissociation.
- To compare cooperativity in carboxyhemoglobin versus oxyhemoglobin.
Main Methods:
- Stopped-flow spectroscopy was used to monitor reactions.
- Species Hb4(CO)x(O2)y were generated in situ.
- Stepwise dissociation rate constants (l4, l3, l2, l1) were measured.
Main Results:
- Stepwise CO dissociation rate constants were determined.
- The overall CO dissociation rate constant is unaffected by 2,3-diphosphoglyceric acid.
- Carboxyhemoglobin exhibits significantly reduced cooperativity compared to oxyhemoglobin.
Conclusions:
- The ligand plays an active role in the rate-limiting step of hemoglobin combination reactions.
- Kinetic data suggest reduced cooperativity in carboxyhemoglobin dissociation.
- pH influences the CO dissociation rate, with a ratio deltal/deltapH of approximately 3.
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