SUMMARY: Growth, nitrogen fixation and acetylene reduction by 301 ( 10,071) were increased with sodium lactate, pyruvate, gluconate or succinate as compared with ethanol, a recommended substrate. Yeast extract could be replaced with (NH)SO; in continuous culture a source of fixed nitrogen could be omitted altogether. Growth, nitrogen fixation and acetylene reduction all increased at lowered pO values. Wholly anaerobic conditions did not support growth. Nitrogen fixation was confirmed isotopically.

Cell-free extracts performed the following reductions: N to NH, H+ to H, CH to CH, KCN to CH, CHNC to CH + CH + CH. An ATP-generating system, Mg, NaSO, and anaerobic conditions during preparation and assay of extracts were required. 3·5 mole ATP were hydrolysed to release 1 mole H. Pyruvate, α-ketobutyrate, α-ketoglutarate, succinate, glucose and glucose-6-phosphate did not replace dithionite. ADP, AMP or high concentrations of ATP inhibited reduction. Activity was associated with a particle which sedimented at 145,000 g over 3·1/2 hr. The nitrogenase system of thus resembles the particulate system of Azotobacter, rather than the soluble pyruvate-utilizing system of .


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