This award will support continued collaborative research between Dr. Alan Hooper, University of Minnesota and Dr. Claude Balny, French National Institute for Health and Medical Research (INSERM), Montpellier. This research is aimed at understanding the chemical functioning of hydroxylamine oxidoreductase (HAO), a key enzyme employed by the nitrifying bacterium Nitrosomonas in aerobic oxidation of soil-bound nitrogen. In the proposed project, the investigators will use the techniques of stopped-flow to study spectral changes in HAO and other chromophoric electron transfer components. They will further study the structure of the active site by comparing the rate of reaction of the subtrates with the rate of reaction of subtrate analogs and binding of competitive inhibitors. In addition, they will investigate the kinds of electron carriers mediating between HAO and the terminal oxidase. Dr. Hooper is an internationally recognized expert on bacterial-nitrification. The expertise of Dr. Balny on stopped-flow in general and on this enzyme system in particular makes continuation of the collaboration appropriate. In addition, Dr. Balny has one of the few facilities in the world where kinetics can be measured at highly controlled temperature and high hydrostatic pressures. The results of this research will contribute to increased understanding of enzymic oxidation of fertilizer ammonia in soils. Beyond fundamental interest to biochemists, this work has important potential applications to understanding the soil nitrogen cycle and to control the agricul- tural loss of soil nitrogen through various denitrification mechanisms.
