Other Nitrogen-Fixing Systems

which can bind dinitrogen (but it is not yet known how), has been determined. It is square planar (10). Consequently, the binuclear model deduced from the kinetics is far from certain. 

One other system shows potential for the production of ammonia and amines from dinitrogen. It was shown several years ago (155) that [(T 5-C5H5)2TiPh2] decomposes thermally via a benzyne intermediate formulated as 42. Such species fix nitrogen. The benzyne complex generated by thermal decomposition as above, or from the reaction of 43 with dinitrogen to form a species formulated as 44. A diphenylacety- 

The area of nonaqueous fixation has been reviewed in detail (344). 

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VI. The Relationship of Lichens to other Nitrogen-Fixing Systems. 303... 

Clostridial ferredoxin was discovered by virtue of its requirement in the oxidation of pyruvate by the clostridial species specifically involved in a nitrogen-fixing system (44). We can now interpret the requirement for pyruvate oxidation as a reaction leading to the formation of reduced ferredoxin, which in turn acted in the reduction of the various substrates, including N2 (45). But there are many other substrates which can be reduced by the reduced ferredoxin—i.e., in the presence of the appropriate enzyme. For example, nitrite may be reduced to ammonia. Reduced ferredoxin can be formed by nonphotosynthetic bacteria by reactions other than puruvate oxidation it can also be formed by the hydrogenase, or by the oxidation of a purine. 

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