Ligand binding properties of horse hemoglobins containing deutero- and mesoheme.
Abstract: The reactions of horse globin reconstituted with proto-, deutero-, and mesoheme have been examined by equilibrium and kinetic methods. In virtually all reactions studied, mesohemoglobin displays the more extreme functional behavior, whereas deuterohemoglobin exhibits behavior which is either very similar to native hemoglobin or intermediate between the two. Our kinetic and equilibrium results indicate that the primary effect of heme modification on the functional properties of hemoglobin is to alter the intrinsic reactivities of the deoxy and liganded conformations. Heme modification does not, however, result in substantial alterations in the conformational equilibrium between the two states. Simple inductive electronic effects of the 2- and 4-substituents of the heme moiety in deutero- and mesohemoglobin are apparently not sufficient to explain the observed equilibrium and kinetic properties completely, which indicates that steric effects of these substituents may also play a role in determining the functional behavior of the hemoglobin molecule.
Publication Date: 1976-01-10 PubMed ID: 1244354
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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 study investigated how modifications to the heme component of horse hemoglobin affected its functional properties. It found that these changes influence the reactivity of the two main conformations of the protein, but not the equilibrium between them. Overall, this suggests that both electronic and steric effects play a role in determining how hemoglobin functions.
Research Overview
This research was undertaken with the specific intent of understanding how modifications to the heme in horse hemoglobin affect the functionality of the molecule. Heme is an essential part of all hemoglobins, including those in horses, and is responsible for the protein’s oxygen-carrying capacity.
The research used equilibrium and kinetic methods to study the behaviors of different versions of hemoglobin where the heme had been changed: deutero-hemoglobin, meso-hemoglobin, and the native (normal) form.
Findings
- Meso-hemoglobin usually exhibited the most extreme changes in function, while deutero-hemoglobin was found to either behave similarly to native hemoglobin or display a behavior that was intermediate to both.
- The functional changes were primarily due to changes in the reactivity of two major conformations of hemoglobin – the deoxy and liganded states. These conformations relate to whether or not the heme part of the molecule is bound to oxygen.
- However, the changes did not drastically alter the conformational equilibrium, the balance between the two states (deoxy and liganded).
Implications
- The basic electronic effects of the heme modifications in deutero- and mesohemoglobin were not enough to fully account for the changes seen in the equilibrium and kinetic properties of the protein.
- This suggests that the physical, or steric, effects of the modifications may also be significant in shaping the functional behavior of the molecule.
- The results provide fundamental insights into how molecular structure and modifications affect the function of proteins such as hemoglobin.
Cite This Article
APA
Seybert DW, Moffat K, Gibson QH.
(1976).
Ligand binding properties of horse hemoglobins containing deutero- and mesoheme.
J Biol Chem, 251(1), 45-52.
Publication
Researcher Affiliations
MeSH Terms
- Animals
- Binding Sites
- Carbon Monoxide / blood
- Heme
- Hemoglobins
- Horses
- Kinetics
- Ligands
- Oxygen / blood
- Protein Binding
Citations
This article has been cited 4 times.- Hannibal L, Page RC, Haque MM, Bolisetty K, Yu Z, Misra S, Stuehr DJ. Dissecting structural and electronic effects in inducible nitric oxide synthase. Biochem J 2015 Apr 1;467(1):153-65.
- Jones EM, Monza E, Balakrishnan G, Blouin GC, Mak PJ, Zhu Q, Kincaid JR, Guallar V, Spiro TG. Differential control of heme reactivity in alpha and beta subunits of hemoglobin: a combined Raman spectroscopic and computational study. J Am Chem Soc 2014 Jul 23;136(29):10325-39.
- Balakrishnan G, Ibrahim M, Mak PJ, Hata J, Kincaid JR, Spiro TG. Linking conformation change to hemoglobin activation via chain-selective time-resolved resonance Raman spectroscopy of protoheme/mesoheme hybrids. J Biol Inorg Chem 2009 Jun;14(5):741-50.
- Gersonde K, Twilfer H, Overkamp M. Bohr-effect and pH-dependence of electron spin resonance spectra of a cobalt-substituted monomeric insect haemoglobin. Biophys Struct Mech 1982;8(3):189-211.
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