9406224 Munck Mossbauer and EPR spectroscopy will be used to study a variety of iron-sulfur proteins and synthetic complexes that mimic the active sites of these proteins. The major focus of the proposed studies will be nitrogenase, with particular emphasis on characterizing intermediates of the catalytic reaction. For these studies protein is available that contains one cluster type (either the cofactor centers or the P-clusters) enriched with the Mossbauer isotope 57Fe whereas the other cluster type contains the Mossbauer-silent 56Fe. The availability of such protein will facilitate the data analyses substantially; moreover, it will allow us to probe the electronic structure of both clusters in considerably more detail. It is also proposed to study carbonmonoxide dehydrogenase and two types of hydrogenases. One of the hydrogenases contains the so-called H- cluster, the stoichiometry of which has not yet been determined in any system studied thus far. Finally, theoretical and experimental studies of 3Fe clusters that occur in proteins and synthetic compounds will be continued. %%% The biological system converts annually in excess of 10 million tons of atmospheric nitrogen into ammonia, which is subsequently incorporated into other cell constituents. Since this process is fundamental to agriculture, many biochemists, biophysicists and geneticists have directed much effort to understand this process on the molecular level. The research of our laboratory has provided a major contribution to the clarification of the structure of the metal centers of nitrogenase. While our past research has addressed the structural aspects of two novel metal clusters in this enzyme, future activities will be directed mostly towards understanding the mechanism of the process, i.e. after having defined the structure involved we wish to elucidate the sequential events occurring during nitrogen fixation. Moreover, we wish to provide structural information to inorganic chemists for the design of catalysts that mimic the biological process. Our struggles with nitrogenase have involved complementary studies that lead to the discovery of new clusters and to fundamentally new insights into magnetochemistry. The proposal studies will address the biochemistry of nitrogenase as well as research of a variety of other related proteins. Our studies of the biological compounds will be complemented by studies of suitable chemical models and theoretical modelling. ***
