PCS: A New Facility for Determining Enzyme Mechanism. Paul Langan, Xinmin Li, Benno Schoenborn, Bioscience Div., Los Alamos National Laboratory, NM 87545.

Scientists have been using the new neutron Protein Crystallography Station (PCS) at Los Alamos to locate functionally important hydrogen atoms and water molecule in enzymes, with a view to designing better drugs. Although X-ray diffraction is the primary tool for determining protein structures, in most cases it cannot be used to locate hydrogen atoms. Hydrogen atoms are the primary motive force in many enzyme reactions. Hydrogen atoms are strong scatterers of neutrons and therefore neutron diffraction is an ideal tool, in some cases the only tool, for determining detailed enzyme mechanisms.

The PCS is run as a designated user facility at the Los Alamos Neutron Science Center. There are two calls for experimental proposals a year, one in March and one in August. Beam time is free and from 10 to 20 experiments can be accommodated each year within a run cycle that stretches from July to February. A deuteration facility is also being established at Los Alamos in order to produce deuterated proteins. For an experiment on the PCS, protein crystals need to be ~1mm3 in volume. Crystals of deuterated proteins however can be significantly smaller. The PCS is the first protein crystallography station to be built at a spallation neutron source and the only resource for neutron protein crystallography in North America. The station exploits the pulsed nature of spallation neutrons and a large electronic detector in order to collect wavelength resolved Laue patterns using all available neutrons in the wavelength range 1A to 5A.

For more information, contact Paul Langan (505) 665-8125, langan_paul@lanl.gov or Benno Schoenborn (505) 665 2033, schoenborn@lanl.gov. This facility is funded by the Department of Energy Office, of Science, Office of Basic Energy Sciences and the Office of Biological and Environmental Research.