Biochemistry Department

Debus Research Group

Professor Debus with Student Image

Welcome to the Debus Research Group


My laboratory is working to understand how plants and algae use sunlight to convert water to molecular oxygen (O2). This process provides nearly the entire supply of O2 on Earth and drives the production of nearly all of Earth’s biomass. The catalytic site contains a Mn4Ca cluster that is located in Photosystem II (PSII) on the lumenal side of the thylakoid membrane. Photosystem II is an integral membrane protein complex that consists of at least 20 different polypeptides and over 50 organic and inorganic cofactors, including chlorophyll. The absorption of light initiates electron transfer reactions within PSII that cause the extraction of electrons and protons from the Mn4Ca cluster, leading to the oxidation of water and the release of O2.

To satisfy the severe energetic and mechanistic constraints of producing O2, the Mn4Ca cluster’s reactivity is tightly controlled by its protein environment. This environment stabilizes the powerful oxidizing equivalents that accumulate on the cluster, optimizes the cluster’s reactivity at each step in the catalytic cycle, lowers the thermodynamic barrier to oxidizing water, and minimizes the release of toxic, partly oxidized intermediates. Our specific goal is identify the amino acid residues that are responsible for this control and to determine the role of each. Our strategy is to combine site-directed mutagenesis and isotopic labeling with spectroscopic characterizations involving Fourier-transform infrared (FTIR), electron paramagnetic resonance (EPR), and time-resolved optical absorption and fluorescence spectroscopies. The primary organism we employ for our studies is the unicellular cyanobacterium, Synechocystis sp. PCC 6803. This organism has essentially the same photosynthetic apparatus as higher plants but its complete genome sequence is available, it can be manipulated genetically more easily than higher plants, and it can be propagated without need for photosystem II. The latter trait permits the study of mutations that would be lethal to most photosynthetic organisms.

Photosystem II is a highly efficient nanomachine. Its Mn4Ca catalyst operates at very high rates (it produces up to 50 molecules of O2 per second), with inexpensive metals, at neutral pH, at ambient temperatures, at ambient pressures, and with high thermodynamic efficiency. It is self assembling and self-repairing in situ. These are all features that would be desirable in synthetic catalysts designed for oxidizing water to O2. No existing synthetic catalyst comes close. Achieving an understanding of how nature produces O2 should provide insight into the design of new generations of synthetic catalysts that convert sunlight and water into useful forms of storable energy.

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University of California, Riverside
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Department of Biochemistry
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Fax: (951) 827-2364
Email: Biochem@ucr.edu

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