This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Using a program of directed evolution experiments we are continuously producing modified versions of enzymes with phosphotriesterase or phosphodiesterase activity towards non-physiological organophosphate substrates. These molecules constitute the main toxic contaminants in certain polluted agricultural or industrial soils. Some of these enzymes are already being used as bioremedial agents capable of cleaning up soiled run-off from farm areas where a high level of pesticide use is required. We wish to use x-ray crystallography to follow the structural changes induced into these enzymes and to use this to understand, at a fundamental level, how small structural changes can have large functional effects.