Nitrogenase Consists of Two Proteins

Carnahan et al. [19] in 1960 also reported N2 fixation with cell-free preparations from C. pasteurianum. They dried their cells in a rotary evaporator at about 40 °C and then extracted them to make their preparations. Their other innovation was to supply high levels of pyruvate to support fixation. The method was reproducible, and we promptly verified their results. [20] Fixation for 3 h in our tests with added pyruvate gave 1.334 atom% 1SN excess. Fixation with other substrates was less vigorous lactate supported fixation to give 0.028 and 0.033 atom% 1SN excess. 

As indicated, a number of laboratories got into the process of purifying the components of nitrogenase, so it is difficult to credit any particular laboratory with first success in the endeavor In 1972,Tsoetol. [22] reported purification of dinitrogenase and dinitrogenase reductase to the highest specific activities reported up to that time. Preparations from different organisms require modification of the techniques. Winter and Burris [23] reported a table of activities of components prepared up to 1976. 

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The nitrogenase system reduces hundreds of millions of kilograms of nitrogen gas to ammonia each year, catalysing tire reaction at ambient temperatures and atmospheric pressure. Nitrogenase consists of two proteins tliat contain... 

The P clusters of nitrogenase. The enzyme nitrogenase consists of two proteins the Fe protein (m.w. 55,000), which contains a single 4Fe-4S center, and the more complex MoFe protein (m.w. 220,000) (48,49). The minimum functional unit of the latter appears to be the half molecule, an asymmetric dimer containing 1 Mo, 14-16 Fe, and 16-18 sulfides. Application of a vast array of spectroscopic methods to the MoFe protein in a variety of oxidation states has led to the conclusion that it contains two types of metal-sulfur cluster in a 2 1 ratio unusual Fe S units termed P clusters, and the protein-bound form of the FeMo-cofactor (50). 

Biological nitrogen fixation is accomplished through the catalytic action of an enzyme known as nitrogenase. Nitrogenase consists of two distinct proteins which contain molybdenum, iron, and sulfur. Because the nitrogenase proteins are denatured by exposure to... 

All species that can fix nitrogen possess the nitrogenase complex. Its structure, similar in all species so far investigated, consists of two proteins called dinitro-genase and dinitrogenase reductase. Dinitrogenase (240 kD), also referred to as Fe-Mo protein, is an a -heterotetramer that contains two molybdenum (Mo) atoms, and 30 iron atoms. It catalyzes the reaction N2 + 8 H+ + 8 —> 2... 

Biological reduction of nitrogen to ammonia ( q. 12) is catalyzed by the nitrogenase enzyme, which consists of two proteins called the Mo-Fe... 

Molybdenum nitrogenase. As mentioned above N. consists of two proteins, both of which are required for activity. One of these proteins contains iron, molybdenum and acid-labile sulfur (Mo-Fe protein, component I, molybdoferredoxin, azofermo) and the other contains iron and labile sulfur (Fe-protein, component II, azoferredoxin. azofer). The two components are present in the ratio 1 Mo-Fe protein 2 Fe-proteins. Both protein components have been isolated and characterized from various nitrogen fixing organisms, and the separated components can be reconstituted to active N. 

The N2-fixing enzyme used by the bacteria is nitrogenase. It consists of two components an Fe protein that contains an [Fe4S4] cluster as a redox system (see p. 106), accepts electrons from ferredoxin, and donates them to the second component, the Fe-Mo protein. This molybdenum-containing protein transfers the electrons to N2 and thus, via various intermediate steps, produces ammonia (NH3). Some of the reducing equivalents are transferred in a side-reaction to In addition to NH3, hydrogen is therefore always produced as well. 

General Considerations. The nitrogenase enzyme consists of two separately isolable proteins—the molybdenum-iron protein (Component I, Fraction I, molybdoferredoxin) and the iron protein (Component II, Fraction II, azoferredoxin). The most recent work on nitrogenase com-... 

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