Physical studies and synthetic modeling of the molybdenum-containing enzyme sulfite oxidase.

Persistent Link:
http://hdl.handle.net/10150/184456
Title:
Physical studies and synthetic modeling of the molybdenum-containing enzyme sulfite oxidase.
Author:
Kipke, Cary Alan.
Issue Date:
1988
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
This research has been directed at the study of both the enzyme sulfite oxidase and molybdenum model chemistry. A modification of a previously published procedure has been used to purify sulfite oxidase in high yield which is well-suited for experiments requiring prosthetically intact enzyme and which is not contaminated with extraneous heme or with other redox active proteins. Laser flash photolysis was used to study the reaction of photoproduced 5-deazariboflavin, lumiflavin, and riboflavin semiquinone radicals with the redox centers of purified sulfite oxidase. Two distinctly different intramolecular electron transfer processes were observed between the molybdenum and heme sites of the enzyme, and these assignments were supported by flash photolysis studies of the cyanide-inactivated enzyme and the sulfite oxidase heme peptide. Microcoulometric experiments on sulfite oxidase have shown that the enzyme requires the addition of three electrons for complete subunit reduction. Midpoint potentials for the Mo(VI)/Mo(V), Mo(V)/Mo(IV), and Fe(III)/Fe(II) couples have been obtained under varied buffer conditions. The midpoint potentials obtained under High-pH and Low-pH conditions provided a means for reductively titrating the enzyme to the Mo(V) oxidation state for EXAFS studies. EXAFS of sulfite oxidase under High-pH and Low-pH conditions have provided the first example of a structural study of the three accessible oxidation states (Mo(VI), Mo(V), and Mo(IV)). A biologically relevant synthetic model for the formation of the Mo(V) Low-pH form of sulfite oxidase has been developed. The Mo(V) model compound closely resembles the minimum coordination environment for the Mo(V) Low-pH form of sulfite oxidase as determined by EXAFS. Using synchrotron radiation, molybdenum L-edge x-ray absorption spectra have been obtained for a variety of oxomolybdenum(V) compounds which serve as models for sulfite oxidase. An attempt has been made to correlate unique features of the molecules to the observed 2P → 4d electronic transitions.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Molybdenum enzymes.; Oxidases.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Chemistry; Graduate College
Degree Grantor:
University of Arizona

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titlePhysical studies and synthetic modeling of the molybdenum-containing enzyme sulfite oxidase.en_US
dc.creatorKipke, Cary Alan.en_US
dc.contributor.authorKipke, Cary Alan.en_US
dc.date.issued1988en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractThis research has been directed at the study of both the enzyme sulfite oxidase and molybdenum model chemistry. A modification of a previously published procedure has been used to purify sulfite oxidase in high yield which is well-suited for experiments requiring prosthetically intact enzyme and which is not contaminated with extraneous heme or with other redox active proteins. Laser flash photolysis was used to study the reaction of photoproduced 5-deazariboflavin, lumiflavin, and riboflavin semiquinone radicals with the redox centers of purified sulfite oxidase. Two distinctly different intramolecular electron transfer processes were observed between the molybdenum and heme sites of the enzyme, and these assignments were supported by flash photolysis studies of the cyanide-inactivated enzyme and the sulfite oxidase heme peptide. Microcoulometric experiments on sulfite oxidase have shown that the enzyme requires the addition of three electrons for complete subunit reduction. Midpoint potentials for the Mo(VI)/Mo(V), Mo(V)/Mo(IV), and Fe(III)/Fe(II) couples have been obtained under varied buffer conditions. The midpoint potentials obtained under High-pH and Low-pH conditions provided a means for reductively titrating the enzyme to the Mo(V) oxidation state for EXAFS studies. EXAFS of sulfite oxidase under High-pH and Low-pH conditions have provided the first example of a structural study of the three accessible oxidation states (Mo(VI), Mo(V), and Mo(IV)). A biologically relevant synthetic model for the formation of the Mo(V) Low-pH form of sulfite oxidase has been developed. The Mo(V) model compound closely resembles the minimum coordination environment for the Mo(V) Low-pH form of sulfite oxidase as determined by EXAFS. Using synchrotron radiation, molybdenum L-edge x-ray absorption spectra have been obtained for a variety of oxomolybdenum(V) compounds which serve as models for sulfite oxidase. An attempt has been made to correlate unique features of the molecules to the observed 2P → 4d electronic transitions.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectMolybdenum enzymes.en_US
dc.subjectOxidases.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineChemistryen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.identifier.proquest8822427en_US
dc.identifier.oclc701329283en_US
All Items in UA Campus Repository are protected by copyright, with all rights reserved, unless otherwise indicated.