Abstract
Cyanobacteria can be used as solar energy converter into hydrogen. We have chosen nitrogenase for the enzyme of hydrogen production because it catalyzes essentially unidirectional production of hydrogen. Our previous studies show that inactivation of uptake hydrogenase (Hup) is effective in enhancing hydrogen production activity. However, a high production activity stage lasted for only about 10 hours. Homocitrate is bound to the catalytic FeMo-cofactor of nitrogenase and is synthesized by NifV. Nitrogenase from Klebsiella pneumoniae nifV mutants showed that it reduced dinitrogen poorly, but acetylene and proton at rates comparable to the wild-type enzyme in the presence of citrate. Nostoc PCC7120 has two nifV genes, and we have created 6 nifV mutants by disruption of either one or both genes on the wild-type and ΔhupL background. The duration of hydrogen high production was longer in the mutant ΔnifV1/ΔhupL than the wild-type. Differential role of two nifV genes is discussed.
