Dissociation of CO from carboxyhemoglobin

The reaction between carboxyhemoglobin and reduced microperoxidase (MP): Hb4(CO)4 + 4MP=Hb4 + 4MPCO, recently reported by us, has been further studied. By generating species Hb4(CO), Hb4(CO)2, and Hb(CO)3 in the stopped flow cuvette by the reaction of dithionite with the species of the general formu...

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Bibliographic Details
Published in:The Journal of biological chemistry 1976-07, Vol.251 (14), p.4267-4272
Main Authors: Sharma, V S, Schmidt, M R, Ranney, H M
Format: Article
Language:English
Subjects:
Carbon Monoxide - blood
Carboxyhemoglobin - metabolism
Hemoglobins - metabolism
Humans
Hydrogen-Ion Concentration
Kinetics
Oxidation-Reduction
Peroxidases - metabolism
Protein Binding
Temperature
Time Factors
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Summary:The reaction between carboxyhemoglobin and reduced microperoxidase (MP): Hb4(CO)4 + 4MP=Hb4 + 4MPCO, recently reported by us, has been further studied. By generating species Hb4(CO), Hb4(CO)2, and Hb(CO)3 in the stopped flow cuvette by the reaction of dithionite with the species of the general formula Hb4(O2)x(CO)y(x + y=4) in the presence of microperoxidase it has been possible to determine the stepwise CO dissociation rate constants l4, l3, l2, and l1. The overall CO dissociation rate constant l, which is the same in this system as l4, is not affected by 2,3-diphosphoglyceric acid. The activation energy of the reaction is 21,400 cal in 15-25 degrees range. The ratio deltal/deltapH is approximately 3 in 6.5 to 7.5 pH range. The kinetic data indicate that, compared to HbO2, the contribution to the cooperativity of the dissociation rate constants of carboxyhemoglobin is greatly reduced. The ligand-dependent differences in the reactions of Hb with CO, O2, and NO suggest that in the combination reactions the ligand plays an active role in the rate-limiting step.
ISSN:0021-9258
1083-351X
DOI:10.1016/S0021-9258(17)33291-X