9307501 Averill Denitrification is a key process in the nitrogen cycle, which controls the amount of nitrogen available for growth of plants, including food crops. Estimates suggest that up to 30% of fertilizer nitrogen is lost via denitrification. A linear pathway for reduction of nitrite to N2 via NO2, NO and N2) seems to be the predominant one, although evidence consistent with direct reduction of NO2 to N20 exists for some organisms. The objective of the proposed research is to elucidate the pathway(s) by which N02 is reduced to N20 in biology. Specific goals include: (1) the use of isotope labelling, chemical trapping, and kinetics studies to examine the mechanism of nitric oxide reductase; (2) the use of genetic techniques to probe nitrite reductase/nitric oxide reductase interactions in denitrifiers, to determine whether a functional nitric oxide reductase is necessary for denitrification by Achromobacter cycloclastes, and to clarify the roles of the metal centers in the Cu- and heme cd1 -containing nitrite reductases; (3) characterization of the mechanism of nitrite reduction by a prototypical eukaryotic denitrifier, the mold Fusarium, which appears to utilize a cytochrome P-450 as a nitrite reductase. %%% The proposed research should result in a fundamental understanding of how diverse organisms utilize nitrogen oxides as terminal electron acceptors. Since denitrifiers are attractive candidates for a variety of biotechnological applications, including waste water remediation, and in addition are important sources of the greenhouse gas N20, these results are likely to have significant practical implications as well. ***
