Keys to help unlock photosynthesis.

Keys to help unlock photosynthesis

"If we fully understood photosynthesis,it might be possible to build solar chemical factories to make food and fuel faster and with higher overall quality than nature can,' says James Norris, a chemist at Argonne (III.) National Laboratory. Though scientists are a long way from understanding photosynthesis that well, they are making important inroads. Among the most recent is the discovery of two key photosynthetic structures.

Argonne scientists have just revealedthe three-dimensional structure of a molecule known as the photosynthetic reaction center. "It's responsible for converting sunlight into chemical energy --the first step in photosynthesis,' explains Marianne Schiffer, a crystallographer in the group.

They worked with Rhodopseudomonassphaeroides, a purple bacterium, for which the constituent subunits of its photosynthetic reaction center were already known. By crystallizing the molecule and studying it with X-ray diffraction techniques, "we now know where they [the subunits] are and how they're related to each other,' Schiffer says. This should help others interpret spectroscopic information for related molecules whose structures have not been characterized, she says, such as the more complicated photosynthetic reaction centers in green plants.

Also using X-ray crystallographictechniques, researchers from three West German institutes report in the Feb. 19 NATURE that they have found the structure of the enzyme (RuBPCase) that initiates the reduction of atmospheric carbon dioxide into organic molecules during photosynthesis. (Reduction can involve either the removal of oxygen or the addition of electrons or hydrogen.)

Writing in the same issue of NATURE,plant physiologist Jim Barber from the Imperial College of Science and Technology in London points out that every molecule of carbon incorporated into some compound in the biosphere originates from the catalytic activity of this enzyme. However, he explains, because the enzyme "does not work at maximum efficiency,' it constrains the productivity of photosynthesis. Many scientists believe it will be necessary to genetically alter this enzyme or its activities if the efficiency of photosynthesis is to be improved, he says. First, however, its structure had to be determined.