Bright x-rays to illuminate a new frontier.

Much of what is known about the atomic structures of proteins and other biological molecules comes from studies of how crystals of these materials deflect X rays. Growing the protein crystals large enough to use with conventional X-ray sources, however, can be a difficult and frustrating task.

This week, researchers expect to get their first chance to use a new, intense source of X rays to begin probing tiny crystals of various proteins. "We've designed our [equipment] to work with extremely small crystals so that even when you don't get the world's best crystals, you can still study them [or parts of them]," says Edwin M. Westbrook, director of the Structural Biology Center at Argonne (Ill.) National Laboratory.

"We're going to test our setup on a variety of crystals over the next month or so," he notes. "By the end of June, we should be reliably on track."

Westbrook heads one of about a dozen collaborations, which include researchers from roughly 100 universities and nearly 50 companies and research institutions, that are gearing up to use Argonne's Advanced Photon Source.

Designed as the world's brightest source of high-energy X rays for studying materials and chemical processes, the facility was dedicated last week.

The U.S. Department of Energy provided $812 million for constructing and operating the Advanced Photon Source. Federal agencies, universities, and other bodies contributed an additional $200 million for instruments and equipment.

When electrons and other charged particles traveling at nearly the speed of light are forced to change direction, they emit electromagnetic radiation (called synchrotron radiation), which emerges as a cone resembling the beam from a car's headlight. As the energy of the particles increases, this cone gets narrower and the average wavelength of the radiation decreases.

In the Advanced Photon Source, the charged particles are positrons, the antimatter counterparts of electrons. These particles are accelerated in stages to an energy of 7 gigaelectronvolts, then injected into a storage ring about 1 kilometer in circumference-large enough to encircle a baseball stadium. The particles circulate there at nearly the speed of light for about 10 hours.

The storage ring is an 80-sided polygon with alternating short and long sides.

At the corners, the bending magnets deflect the circulating positrons and stimulate the emission of X rays with a broad range of wavelengths. Along most of the straight sections, the positrons pass through a gauntlet of magnets that jiggle the particles back and forth in a tight, snaking path. Each change in direction produces an intense burst of high-energy X rays with a well-defined wavelength, which can then be directed to the specific sample.

The Advanced Photon Source allows as many as 35 research teams to conduct experiments simultaneously. Each research group has access to two X-ray beams, one from a corner and the other from the undulator magnets of a straight section of the storage ring. By adjusting the magnets, the researchers can tailor the X-ray beams to a particular experiment.

Groups already preparing experiments plan to take advantage of this unique X-ray source to do highly detailed protein crystallography; obtain new views of enzymes, toxins, viral proteins, and other biological molecules; and produce movies of changes in atomic and molecular arrangements as polymers or semiconductors form.