Equilibria of organic phosphates with horse oxyhemoglobin.
Abstract: Organic phosphates, ATP, AMP, and 2,3-di-phosphoglycerate (DPG) were interacted with horse oxyhemo-globin. Binding parameters were obtained by means of dialysis equilibrium in buffers at 5°, and from calorimetry at 5 and 25°, all in the pH mom 6.5-7.3. The calorimetric results were evaluated assuming a single strong site, and assuming that the pH shifts which occur in the absence of added salt are due to electrostatic effects and not to changes in side-chain titration, upon mixing samples previously ad-justed to the same pH. There was obtained for ATP and 2,3- diphosphoglycerate. respectively, AG° — —6.5 and —4.9 kcal molt, 4H° — —5.2 and —9.1 kcal mol-,, and AS° - +5 and —14 cal deg-' mol-', at pH 6.9 and 25°. These binding parameters are for the case of no added salt. In dialysis equilibrium experiments, buffer and supporting elec-trolyte were used. In that case, the results indicate strong
competition by inorganic phosphate, lesser competition by chloride, while cacodylate possibly is noncompetitive or nearly so. Competition by salt ions also is manifest in calor'. etry of organic phosphate binding. Equilibria of AMP, in the presence of orthophosphate, may engage in a somewhat different mechanism involving the protein. There appears to be chemical linkage between binding sites, when AMP is the substrate. There are indications that for organic phosphates, there exists more than one site available on oxyhemoglobin. However there is only one strong site. Certain of the pH-de-pendent phenomena were roughly accounted for by electro-static effects using the smeared charge model. Calorimetry at 5°, compared to 25°, indicates a ;SC, of binding of +260 cal deg-, mot-, for ATP-deionixed oxyhemoglobin interac-tion, and a ACt. of about +100 cal deg-, mol-, for DPG in-teraction.
Publication Date: 1972-12-05 PubMed ID: 4655249DOI: 10.1021/bi00775a004Google Scholar: Lookup
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- Journal Article
Summary
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The research investigates how horse oxyhemoglobin reacts with organic phosphates like ATP, AMP and 2,3-diphosphoglycerate (DPG). The researchers discovered that these compounds bind differently to oxyhemoglobin, with inorganic phosphate showing the strongest competition, while AMP might engage in a different mechanism with the protein.
Methodology
- The team explored the interaction between organic phosphates and horse oxyhemoglobin using dialysis equilibrium in buffers at 5 degrees Celsius and pH ranging from 6.5 to 7.3.
- They also performed calorimetry at 5 and 25 degrees Celsius.
- In their analysis, the researchers based their assumptions on the existence of single strong site, with pH shifts that occur due to electrostatic effects rather than changes in side-chain titration.
Findings
- The results revealed specific binding parameters for ATP and 2,3-diphosphoglycerate respectively.
- The researchers noticed that the binding parameters changed in the absence of added salt, while dialysis equilibrium experiments conducted with buffer and supporting electrolyte showed different results.
- Inorganic phosphate demonstrated strong competition, while chloride showed less competition. Cacodylate seemed to be either noncompetitive or almost so.
Specific Substrate Observations
- The study reported that AMP, in the presence of orthophosphate, may have a different mechanism involving the protein, suggesting a chemical link between binding sites when AMP is the substrate.
- For organic phosphates, the research indicates that there may be more than one available site on oxyhemoglobin, although only one strong site was identified.
pH-Dependent Phenomena
- The researchers accounted for certain pH-dependent occurrences by considering electrostatic effects using the smeared charge model.
- Calorimetry conducted at 5 degrees, versus 25 degrees, demonstrated a significantly higher change in binding parameters for ATP-deionized oxyhemoglobin interaction and for DPG interaction.
The research provides detailed insight into the relationship between organic phosphates and horse oxyhemoglobin, and presents a potential space for further exploration and understanding of these interactions.
Cite This Article
APA
Hedlund B, Danielson C, Lovrien R.
(1972).
Equilibria of organic phosphates with horse oxyhemoglobin.
Biochemistry, 11(25), 4660-4668.
https://doi.org/10.1021/bi00775a004 Publication
Researcher Affiliations
MeSH Terms
- Adenosine Monophosphate
- Adenosine Triphosphate
- Animals
- Arsenic
- Binding Sites
- Binding, Competitive
- Calorimetry
- Chlorides
- Dialysis
- Diphosphoglyceric Acids
- Glyceric Acids
- Hemoglobins
- Horses
- Hydrogen-Ion Concentration
- Mathematics
- Organophosphorus Compounds
- Osmolar Concentration
- Oxyhemoglobins
- Phosphates
- Protein Binding
- Sodium Chloride
- Thermodynamics
Citations
This article has been cited 2 times.- Haire RN, Hedlund BE. Thermodynamic aspects of the linkage between binding of chloride and oxygen to human hemoglobin. Proc Natl Acad Sci U S A 1977 Oct;74(10):4135-8.
- Coates ML. Hemoglobin function in the vertebrates: an evolutionary model. J Mol Evol 1975 Dec 29;6(4):285-307.
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