News & Events

Alice Haddy, Ph.D.

Posted on October 6, 2017


Date - October 6, 2017
1:00 pm - 2:00 pm


Professor of Biophysical Chemistry
Department of Chemistry & Biochemistry
University of North Carolina Greensboro

Talk Title: “The role of chloride in photosystem II, or how chloride helped fill the world with oxygen so animals could breath”


The membrane-bound protein complex photosystem II is one of the major energy-transducing enzymes in nature. Using light energy, it promotes photosynthetic electron transfer that results in the capture of light energy for the eventual use by nearly all life forms on Earth. At the same time, it produces the essentially all of the molecular oxygen in the atmosphere of Earth. Chloride has a unique role in the regulation of the activity of photosystem II, which contains a catalytic Mn4CaO5 cluster where oxygen is produced by oxidation of water. We have explored the characteristics of the chloride requirement using a variety of anion substitutes and pH dependence studies. The effects of these conditions have been characterized using enzyme kinetics analyses during full catalytic turnover. In addition, the presence of radicals from the Mn4CaO5 cluster and a nearby tyrosine residue have been detected by electron paramagnetic resonance (EPR) spectroscopy at various points of the catalytic cycle. These studies help reveal details about how chloride affects the coupling between the Mn ions of the catalytic cluster and facilitates proton coordination during oxygen production, so that its regulatory role may be better understood.