Nitrogenase complex

MgATP hydrolysis and, 47 189-191 nitrogenase complex, 47 186-189 substrates, 47 192-202 molybdenum iron proteins, 47 161, 166-174, 176-183, 191-192 structure, 47 162-164, 166-170 nitrogen fixation role, 36 78 in nitrogen fixation systems, 27 265-266 noncomplementary reactions with Sn", 10 215... 

Fixation of N2 as NH3 is carried out by the nitrogenase complex, in a reaction that requires ATP. The nitrogenase complex is highly labile in the presence of 02. 

Terms in bold are defined in the nitrogen cycle 834 nitrogen fixation 834 symbionts 834 nitrogenase complex 835 leghemoglobin 836 glutamine synthetase 838 glutamate synthase 838 glutamine amidotransferases 840 5-phosphoribosyl-l-... 

Nitrogen fixation is the conversion of N2 gas into ammonia, a process carried out by some soil bacteria, cyanobacteria and the symbiotic bacteria Rhizobium that invade the root nodules of leguminous plants. This process is carried out by the nitrogenase complex, which consists of a reductase and an iron-molybdenum-containing nitrogenase. At least 16 ATP molecules are hydrolyzed to form two molecules of ammonia. Leghemoglobin is used to protect the nitrogenase in the Rhizobium from inactivation by 02. 

The principle advances in the area has been made using x-ray structural analysis. Crystallographic data have been first produced for the nitrogenase complex of FeP (A2) and FeMoP (Al) from Azotobacter vinelandii (Kim and Rees, 1992) and for the corresponding complex of Cp2 and Cpl from Clostridium pasterianum (Bolen et al., 1993), ). A 1.6 A resolution X-ray crystallographic structure of Klebsiella pneumoniae proteins has been recently reported (Mayer et al., 1999) It was shown that FeMoco sites in Al, Cpl, and Kpl are 70 A apart and FeMoco and P clusters are separated by about 19 A. X-ray structures of the nitrogenase complex and the active site clusters are presented in (Figs. 3.2-3.4). 

Figure 3.6. Schematic presentation of photoreduction of the nitrogenase complex (see details in text)...

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