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Mössbauer and Spectroscopic Studies of Yeast Cytochrome Oxidase


Wang, Hsin (1987) Mössbauer and Spectroscopic Studies of Yeast Cytochrome Oxidase. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/jfrs-d493.


Cytochrome oxidase from baker's yeast is investigated by Mössbauer spectroscopy, complemented by EPR, flash photolysis, and spectroelectrochemical studies. While the Mössbauer spectrum of cytochrome α can be described with one set of parameters, at least three components were identified for cytochrome α3 in the native enzyme: a functional coupled site, a high spin ferric ion with the antiferromagnetic coupling disrupted, and a low spin ferrous ion. Photolysis experiments indicate that the CO-recombination at the functional cytochrome α3 in yeast is a slow process with an activation energy of 33 kJ/mol, similar to that observed previously in the beef heart enzyme. The structure of this site is therefore very similar in both enzymes. However, the Mössbauer spectrum of the this site in yeast cannot be explained by the current spin Hamiltonian model that describes the widely accepted spin-coupling hypothesis. The shortcoming of this model is pointed out and discussed. The assignment of the reduced low spin heme to a degraded form of cytochrome α3 is strengthened by photolysis studies, which reveal a second fast CO-rebinding site with a peak activation energy (13 kJ/mol) similar to that of myoglobin, and by spectroelectrochemical measurements, which demonstrate that the redox potential of the degraded cytochrome α is low rather than high as previously thought. Based on these findings in yeast oxidase and previous inactivation reports on beef heart oxidase, a global change in the structures of all of the metal centers during denaturation is suggested. The redox behavior of the normal cytochrome α in the CO-inhibited enzyme is well-explained by a 2-site interaction model which has also been applied successfully in the beef heart enzyme. The redox potential of cytochrome α in yeast is found to be roughly 45 mV higher than that in beef heart. A comparative EPR and Mössbauer study of the reoxidation of the fully-reduced yeast enzyme is also presented. The reoxidation course is well-described by the mechanism proposed for the beef heart enzyme and a few intermediates are suggested by the Mössbauer study.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Chemistry
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemistry
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Hopfield, John J.
Thesis Committee:
  • Hopfield, John J. (chair)
  • Chan, Sunney I.
  • Collins, Terrence J.
  • Gray, Harry B.
Defense Date:19 September 1986
Record Number:CaltechTHESIS:10302019-125418569
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:11874
Deposited By: Mel Ray
Deposited On:30 Oct 2019 23:22
Last Modified:16 Apr 2021 23:10

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