Research in Photosynthesis
Sunlight is the ultimate source of energy for most organisms on Earth. In plants, algae and cyanobacteria, the energy of light is used to synthesize carbohydrates from CO2, resulting in the byproduct of atmospheric O2. My research group focuses on the study of Type I (iron-sulfur) reaction centers, including Photosystem I of cyanobacteria (Figure 1.1) and plants, and the reaction centers of the strictly anaerobic heliobacteria and green sulfur bacteria. My students and I work to uncover the genes, polypeptides, and cofactors that are involved in the structure, function, and assembly of Type I reaction centers. To accomplish these goals, we employ molecular biological techniques such as site-directed mutagenesis and secondary suppressor screening, biochemical techniques such as resolution and reconstitution of proteins and cofactors, and biophysical techniques such as magnetic resonance spectroscopy and time-resolved optical spectroscopy.
Figure 1.1. View form the stromal surface of the Photosytem I trimer from Thermosynechococcus elongatus. Figure from P. Jordan, Ph.D. thesis, Berlin.
Why Study Photosynthesis?
The world’s dependence on fossil fuels for energy is fraught with a variety of environmental, social and political problems. Looming over the horizon is the eventual depletion of the inexpensive oil and natural gas that currently powers the world’s economy. The already-noticeable onset of global warming caused by the build-up of atmospheric carbon dioxide and methane threatens the world’s climate (Figure 1.2). The solution to the energy problem is to construct an economy based on hydrogen as a primary fuel. Unlike the combustion of fossil fuels, which produces carbon dioxide, the combustion of hydrogen produces only water as byproduct.
Figure 1.2. The green color depicts the portion of the Earth's
land surface that supports oxygenic photosynthesis.
The trick is to synthesize hydrogen without using fossil fuels as an intermediate; i.e. directly with the use of solar, wind or tidal power. The product of Photosystem I is NADPH, a molecule with about the same standard free energy of combustion as hydrogen. Work in my laboratory is aimed ultimately at modifying the acceptor system of Photosystem I so that the product is H2 rather than the biological reductant NADPH.
If you would like to learn more about the light reactions of photosynthesis and especially Photosystem I, I have written a chapter called “Photosynthetic Electron Transfer: So Little Time, So Much to Do” for ‘Biophysics Textbook On Line.
Search the MEDLINE database at PubMed for articles by J Golbeck