Electron Extraction from the A1a and A1b sites of Photosystem I

Open Access
Author:
Gorka, Michael J
Graduate Program:
Chemistry
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
July 31, 2015
Committee Members:
  • John H Golbeck, Dissertation Advisor
  • John H Golbeck, Committee Chair
  • Christine Dolan Keating, Committee Member
  • David D Boehr, Committee Member
  • Donald Ashley Bryant, Committee Member
  • Wayne Roger Curtis, Special Member
Keywords:
  • Photosystem I
  • Dihydrogen
  • Quinone
Abstract:
This dissertation describes an analysis of the kinetic properties of cyanobacterial Photosystem I (PS I) and how the principles learned can be applied for the general production of biofuels. First, I describe development of a robust and unique organic/inorganic photobiochemical nanoconstruct formed by the coupling of PS I and an inorganic thiolate stabilized Pt nanoparticle via a molecular wire. PS I serves to harvest and store light energy, while the Pt nanoparticle catalyzes the reduction of two protons to dihydrogen utilizing the electrons donated from PS I. While the idea to use a molecular wire to facilitate electron exaction from PS I is not new, this is the first successful work in which these two modules are tethered from the A1A and A1B (quinone) sites instead of from the terminal FB iron-sulfur cluster. Using the menB mutant from PS I that contains a displaceable plastoquinone in the A1A and A1B binding sites, I reconstituted the site with a phylloquinone-like molecule that contains a terminated thiol bound to a Pt nanoparticle. I investigate how this system functions, as electron transfer to the Pt nanoparticle is unfavorable relative to both forward electron transfer and charge recombination. I proposed that dihydrogen production is made possible by suppressing the charge recombination channel via rapid reduction of P700+ from an external donor. This proposal was tested by starting with intact PS I and sequentially removing the iron-sulfur clusters, measuring the rate of P700+ reduction, and correlating dihydrogen production to a specific concentration of cytochrome c6. Second, I investigate the electron transfer properties of PS I embedded in a room temperature glass provided by trehalose. I show that not only does immobilization have a significant impact on the electron transfer rates, but also that iv the induced changes are nearly identical to those seen in low temperature glasses provided by glycerol. This method provides a unique opportunity to mimic low temperatures effects on PS I at room temperature as well as providing a means for long term stabilization of protein function at room temperature.