1. Introduction
H2 metabolism in N2-fixing cyanobacteria may involve three
enzymes: nitrogenase, the uptake hydrogenase and the bidirectional
Hox-hydrogenase. The nitrogenase complex consists of two
complexes, dinitrogenase (encoded by nifD and nifK) and dinitrogenase
reductase (encoded by nifH). Nitrogenase catalyzes H2
production concomitantly with N2-fixation with a minimum of
25% of the electrons used for H2 production.