Nitrogen fixation energy cost

N2 Fixation The NH3 produced by the bacteroids has first to be exported via bacteroid and host membranes to cytosol of the nodule and then possibly assimilated within various organelles or cell types to form amino acids, amides, or ureides for export in the xylem. Considering the numbers of nitrogen atoms exported per compound, costs of 3, 2, and 1.75 ATP/nitrogen transported would appear to be reasonable estimates of the energy cost for the transport of amino acids, amides, and ureides, respectively. Added to this would be any costs in transmembrane transfers of ammonia from bacteroid to plant. 

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