Chemical evolution of a nitrogenase model. VII. The reduction of nitrogen
Nitrogenase model systems composed of molybdate and thiol ligands such as L(+)-cysteine reduce molecular nitrogen to ammonia slowly in the presence of NaBH/sub 4/ as the reducing agent. In the presence of substrate amounts of ATP, the reduction of nitrogen is significantly stimulated but leads to the accumulation of diimide in the reaction solutions. The diimide decomposes or disproportionates to nitrogen, hydrogen, and hydrazine and is not reduced as such. The ammonia produced in all reactions arises primarily from the reduction of hydrazine. These observations were confirmed by independent experiments with diimide generated by the decomposition of azodicarboxylate and with hydrazine. Diimide is not a substrate for molybdothiol catalyst systems, while hydrazine is catalytically reduced to ammonia. Molybdothiol catalysts promote D/sub 2/-- H/ sup +/ exchange most efficiently in the presence of nitrogen as the substrate; they thus parallel nitrogenase also in this respect. The D/sub 2/-H/sup +/ exchange reaction is prssumably linked to the formation and decomposition of diimide in both the nitrogerase enzyme and its models. The current molybdothiol model systems were furthermore expanded to include ferredoxin-type complexes as electron-transfer catalysts. This provided new catalytically active systems containing molybdenum, iron, labile sulfide, and RSH components in proportions similar to that observed in native nitrogenase. The new model systems catalyze the reduction of, e.g., acetylene efficiently even with S/sub 2/O/sub 4/ as the reducing agent and thus duplicate nitrogenase in yet another important respect. (12 tables, 6 figures) (auth)
- Research Organization:
- Univ. of California, San Diego, La Jolla
- Sponsoring Organization:
- USDOE
- NSA Number:
- NSA-29-018126
- OSTI ID:
- 4346769
- Journal Information:
- J. Amer. Chem. Soc., v. 96, no. 3, pp. 641-652, Other Information: Orig. Receipt Date: 30-JUN-74
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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