Energy expenditure for cyclic retention of NH3/NH4+ during N2 fixation by Klebsiella pneumoniae.

The permeability coefficient for NH3 through bacterial membranes was determined to be around 2 X 10(-3) cm X s-1. This value was used to calculate the outward diffusion of NH3 from intracellular pools and the energy costs for reabsorption as NH4+. For an N2-fixing continuous culture of Klebsiella pneumoniae an energy expenditure of around 4 ATP per NH3 produced was calculated, thus increasing significantly the energy requirement for N2 fixation in vivo.