Quantum yields and the mechanism of ligand binding to heme proteins
Ligand binding to several naturally occurring and engineered myoglobins and hemoglobins was examined. Overall and germinate rate constants and quantum yields were determined at pH 7, 20$\sp\circ$C for O$\sb2$, NO, CO, and a set of n-series and $\alpha$-substituted alkyl isocyanide complexes of sperm...
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ftriceuniv:oai:scholarship.rice.edu:1911/16287 2023-05-15T18:26:44+02:00 Quantum yields and the mechanism of ligand binding to heme proteins Rohlfs, Ronald James 1989 application/pdf https://hdl.handle.net/1911/16287 eng eng Rohlfs, Ronald James. "Quantum yields and the mechanism of ligand binding to heme proteins." (1989) Diss., Rice University. https://hdl.handle.net/1911/16287 . https://hdl.handle.net/1911/16287 Thesis Biochem. 1989 Rohlfs Biochemistry Thesis Text 1989 ftriceuniv 2022-08-09T20:52:41Z Ligand binding to several naturally occurring and engineered myoglobins and hemoglobins was examined. Overall and germinate rate constants and quantum yields were determined at pH 7, 20$\sp\circ$C for O$\sb2$, NO, CO, and a set of n-series and $\alpha$-substituted alkyl isocyanide complexes of sperm whale myoglobin, isolated $\alpha$ and $\beta$ hemoglobin chains, soybean leghemoglobin, and monomeric hemoglobin component II from Glycera dibranchiata using a 30 ns dye laser pulse and a 0.5 ms xenon flash. Overall rates and quantum yields for several sperm whale myoglobin complexes were compared to parameters obtained for site directed mutants of this protein, in which His-E7 was replaced by one of several different amino acids. Results were analyzed using a linear three step reaction scheme, HbX$\rightleftharpoons$B$\rightleftharpoons$C$\rightleftharpoons$H $+$ X, where X is ligand free in solution, H and HX are unliganded and liganded heme protein respectively, B represents a geminate state in which the ligand is in the distal pocket but not covalently bound to the iron atom, and C is a state in which the ligand is still embedded in the protein but further away from the heme group. The results indicate that low overall quantum yields are due to rapid rates of geminate recombination relative to rates of ligand escape to solvent rather than a low intrinsic photophysical yield. For all CO complexes, Q is large and the rate limiting step for association is iron-ligand bond formation and dissociation is rate limited by thermal bond disruption. For O$\sb2$, NO, and most of the isonitrile complexes, Q is small ($\leq$0.2) indicating the association rate is approximately equal to the rate of ligand migration to state B, and dissociation is limited by escape from the protein. Studies of the site directed mutants of Mb show that the E7 residue acts as a steric barrier for isonitriles. In contrast, the polarity of the E7 side chain is more important in determining the rate and equilibrium constants for O$\sb2$ and CO ... Thesis Sperm whale Rice University: Digital Scholarship Archive |
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Rice University: Digital Scholarship Archive |
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English |
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Biochemistry |
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Biochemistry Rohlfs, Ronald James Quantum yields and the mechanism of ligand binding to heme proteins |
topic_facet |
Biochemistry |
description |
Ligand binding to several naturally occurring and engineered myoglobins and hemoglobins was examined. Overall and germinate rate constants and quantum yields were determined at pH 7, 20$\sp\circ$C for O$\sb2$, NO, CO, and a set of n-series and $\alpha$-substituted alkyl isocyanide complexes of sperm whale myoglobin, isolated $\alpha$ and $\beta$ hemoglobin chains, soybean leghemoglobin, and monomeric hemoglobin component II from Glycera dibranchiata using a 30 ns dye laser pulse and a 0.5 ms xenon flash. Overall rates and quantum yields for several sperm whale myoglobin complexes were compared to parameters obtained for site directed mutants of this protein, in which His-E7 was replaced by one of several different amino acids. Results were analyzed using a linear three step reaction scheme, HbX$\rightleftharpoons$B$\rightleftharpoons$C$\rightleftharpoons$H $+$ X, where X is ligand free in solution, H and HX are unliganded and liganded heme protein respectively, B represents a geminate state in which the ligand is in the distal pocket but not covalently bound to the iron atom, and C is a state in which the ligand is still embedded in the protein but further away from the heme group. The results indicate that low overall quantum yields are due to rapid rates of geminate recombination relative to rates of ligand escape to solvent rather than a low intrinsic photophysical yield. For all CO complexes, Q is large and the rate limiting step for association is iron-ligand bond formation and dissociation is rate limited by thermal bond disruption. For O$\sb2$, NO, and most of the isonitrile complexes, Q is small ($\leq$0.2) indicating the association rate is approximately equal to the rate of ligand migration to state B, and dissociation is limited by escape from the protein. Studies of the site directed mutants of Mb show that the E7 residue acts as a steric barrier for isonitriles. In contrast, the polarity of the E7 side chain is more important in determining the rate and equilibrium constants for O$\sb2$ and CO ... |
format |
Thesis |
author |
Rohlfs, Ronald James |
author_facet |
Rohlfs, Ronald James |
author_sort |
Rohlfs, Ronald James |
title |
Quantum yields and the mechanism of ligand binding to heme proteins |
title_short |
Quantum yields and the mechanism of ligand binding to heme proteins |
title_full |
Quantum yields and the mechanism of ligand binding to heme proteins |
title_fullStr |
Quantum yields and the mechanism of ligand binding to heme proteins |
title_full_unstemmed |
Quantum yields and the mechanism of ligand binding to heme proteins |
title_sort |
quantum yields and the mechanism of ligand binding to heme proteins |
publishDate |
1989 |
url |
https://hdl.handle.net/1911/16287 |
genre |
Sperm whale |
genre_facet |
Sperm whale |
op_relation |
Rohlfs, Ronald James. "Quantum yields and the mechanism of ligand binding to heme proteins." (1989) Diss., Rice University. https://hdl.handle.net/1911/16287 . https://hdl.handle.net/1911/16287 Thesis Biochem. 1989 Rohlfs |
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1766208703898320896 |