The apparent ATP requirement for nitrogen fixation in growing Klebsiella pneumoniae.

The apparent ATP requirement for N2 fixation in Klebsiella pneumoniae was high (the ATP/N2 molar ratio was 29 when estimated in anaerobic glucose-limited chemostat cultures) compared with that determined previously in Azotobacter chroococcum and in Clostridium pasteurianum. The high value was probably not due to unfavourable temperature, phosphate concentration or pH. The apparent ATP requirement for N2 fixation was probably no lower in 02-limited chemostat cultures than in anaerobic glucose-limited chemostat cultures. When hydrogen was introduced into the atmosphere over the anaerobic glucose-limited chemostate culture, there was an increase in the apparent ATP requirement for N2 fixation and in the activity of nitrogenase in intact organisms. A comparison of these increases suggests that some ATP is wasted by the ATP-dependent H2-evolving activity of nitrogenase.