Electronic and steric factors affecting ligand binding: horse hemoglobins containing 2,4-dimethyldeuteroheme and 2,4-dibromodeuteroheme.
Abstract: Horse globin has been recombined with 2,4-dimethyldeuteroheme and 2,4-dibromodeuteroheme to yield the corresponding reconstituted hemoglobins, and the ligand binding reactions of these reconstituted hemoglobins have been examined in detail. Both hemoglobins exhibit relatively high n values, but 2,4-dimethyldeuterohemoglobin displays a consistently higher oxygen affinity than native hemoglobin, whereas the oxygen affinity of 2,4-dibromodeuterohemoglobin is consistently lower than that of native hemoglobin. The rate constants l’, and 1’4 for the binding of the first and fourth molecules of CO, respectively, for both reconstituted hemoglobins are not markedly different from those of native hemoglobin. In contrast, the kinetic rate constants for oxygen dissociation from these hemoglobins are appreciably altered. The rate constants for oxygen dissociation in the presence of dithionite for 2,4-dimethyl- and 2,4-dibromodeuterohemoglobin are 8 S’ and 72 s-l, respectively; the corresponding rate constant for native hemoglobin is 33 s-l. Analogous results were obtained for the dissociation of oxygen in the presence of dithionite and CO. The pK of the acid-alkaline transition in the Met forms of the two reconstituted hemoglobins (pK’) was also appreciably different for 2,4-dimethyl- and 2,4-dibromodeuterohemoglobin.
Publication Date: 1977-06-25 PubMed ID: 16926
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- Journal Article
- Research Support
- U.S. Gov't
- Non-P.H.S.
- Research Support
- U.S. Gov't
- P.H.S.
Summary
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This research paper examines how electronic and steric factors affect ligand binding in horse hemoglobin recombined with 2,4-dimethyldeuteroheme and 2,4-dibromodeuteroheme, assessing the oxygen affinity and the kinetic rate constants for oxygen dissociation in these hemoglobins.
Research Procedure
- Horse globin was recombined with 2,4-dimethyldeuteroheme and 2,4-dibromodeuteroheme to create the corresponding reconstituted hemoglobins.
- The ligand binding reactions of these reconstituted hemoglobins were analyzed in detail.
Examination of Oxygen Affinity
- The researchers note that both reconstituted hemoglobins have high n values, a commonly used measure in chemical equilibrium studies.
- However, the 2,4-dimethyldeuterohemoglobin exhibits a consistently higher oxygen affinity compared to native (natural) horse hemoglobin. This suggests that it can bond with oxygen more easily.
- Conversely, 2,4-dibromodeuterohemoglobin shows consistently lower oxygen affinity than the native horse hemoglobin, indicating a lesser readiness to bond with oxygen.
Kinetic Rate Constants for Ligand Binding and Dissociation
- The rate constants (l’ and 1’4) for the binding of the first and fourth molecules of carbon monoxide (CO) respectively for both reconstituted hemoglobins do not deviate significantly from those of the native hemoglobin.
- However, the kinetic rate constants for oxygen dissociation from these reconstituted hemoglobins are noticeably altered.
- The rate constants for oxygen dissociation in the presence of dithionite for 2,4-dimethyl- and 2,4-dibromodeuterohemoglobin are 8s-1 and 72s-1 respectively, compared to 33s-1 for native hemoglobin.
Acid-Alkaline Transition in Reconstituted Hemoglobins
- Furthermore, the study found that the pK of the acid-alkaline transition in the Met forms of the two reconstituted hemoglobins (pK’) also varied substantially between 2,4-dimethyl- and 2,4-dibromodeuterohemoglobin.
- pK is a measure of acid strength. The “Met forms” refers to the methemoglobin forms (oxidized form) of the reconstituted hemoglobins.
Cite This Article
APA
Seybert DW, Moffat K, Gibson QH, Chang CK.
(1977).
Electronic and steric factors affecting ligand binding: horse hemoglobins containing 2,4-dimethyldeuteroheme and 2,4-dibromodeuteroheme.
J Biol Chem, 252(12), 4225-4231.
Publication
Researcher Affiliations
MeSH Terms
- Animals
- Carbon Monoxide
- Heme / analogs & derivatives
- Hemoglobins / metabolism
- Horses
- Hydrogen-Ion Concentration
- Ligands
- Oxygen
- Protein Binding
- Spectrophotometry
Citations
This article has been cited 1 times.- Makino R, Park SY, Obayashi E, Iizuka T, Hori H, Shiro Y. Oxygen binding and redox properties of the heme in soluble guanylate cyclase: implications for the mechanism of ligand discrimination. J Biol Chem 2011 May 6;286(18):15678-87.
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