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John Golbeck

Professor of Biochemistry and Biophysics
Professor of Chemistry

310 South Frear Laboratory, University Park, PA 16802
Phone: (814) 865-1163
Fax: (814) 863-7024
E-mail: jhg5@psu.edu

B.S. in Chemistry from Valparaiso University
Ph.D. in Chemistry from Indiana University

Golbeck Lab Web Site

Structure/Function Studies of Photosystem I in Cyanobacteria
Photosystem I is a a light-driven plastocyanin: ferredoxin oxidoreductase that uses the 1.78 eV available in a red (700 nm) photon to drive the 800 mV thermodynamically uphill electron transfer between plastocyanin (E1/2 +380 mV) and ferredoxin (E1/2 -420 mV). The reaction center contains 12 polypeptides in cyanobacteria, but the core is a heterodimer of the PsaA and PsaB polypeptides that contain the spectroscopically-identified electron transfer cofactors P700 (a chlorophyll a/a’ heterodimer); A0 (a chlorophyll a monomer); A1 (a phylloquinone); and FX, (a [4Fe-4S] cluster). The 2.5 Å resolution X-ray crystal structure shows three pairs of chlorophyll a molecules and a pair of phylloquinones arranged in two pseudo C2-symmetric branches that diverge at the chlorophyll a/a’ heterodimer P700 and re-converge at the interpolypeptide FX cluster (Figure 2.1.). One area of my research is to determine is whether only the A- branch (or both) of cofactors are active in electron transfer from P700 to FX. Another is to develop biological methods to replace the native phylloquinone with foreign quinones for the purpose of determining which protein factors are important for conferring redox potentials. A third project is to model the reaction center mathematically to relate redox potentials to equilibrium constants and electron transfer rates.
	Figure 2.1. The electron transfer cofactors in cyanobacterial Photosystem I. Note that the A- and B- side cofactors are related by C2 symmetry and that there are potentially two routes for electron transfer from P700 to FX (pdb entry 1JB0).
If you would like to learn more about individual projects, please follow these links:

Directionality of Electron Transfer Among the Bifurcating Electron Transfer Chain Biological Substitution of Phylloquinone with Foreign Quinones in the A1 Site Modeling of Electron Transfer Reactions in Photosystem I