Nitrogenase-Hydrogenase Interrelationship

Rhizobium and Legume Root Nodulation
Leguminous Plants
The Discovery of Symbiotic Nitrogen Fixation
Rhizobium Classification
Cultural Characteristics
Genetics
Flavonoids Induce Nodualation
Novel Approaches to Extend Root Nodulation
Ecology
Infection
Lectins
Structure of the Nodule
Function of the Nodule
Nitrogenase Hydrogenase Interrelationship
Stem Nodulating Legumes
Factors Affecting Nodulation
Temperature and Light
Hydrogen Ion Concentration
Mineral Nutrition

Nitrogenase-Hydrogenase Interrelationship

Nitrogenase-Hydrogenase Interrelationship
Nitrogenases from all known sources and systems catalyze hydrogen production to varying degrees during nitrogen-fixation. One of the important factors influencing the magnitude of hydrogen evolution in N₂ fixing systems is the operation of hydrogen recycling enzyme known as uptake hydrogenase. It is known that most of the nitrogen-fixing bacteria recycle the hydrogen produced during nitrogen fixation but many strains of rhizobia lack an effective uptake hydrogenase.

In nature, there are both hydrogenase positive (Hup⁺) and negative (Hup^-) strains and, the nodules formed by these strains differ in the rate of H₂ evolution. Some nodules evolve more hydrogen whereas others evolve less. Under experimental conditions inoculants made by Hup⁺ strains increase yield from 16-32% over Hup^- strains accompanied by increased total nitrogen accretions in shoots and grains varying from 8 to 49%. Such benefits from Hup⁺ strains have been clearly demonstrated in soybean-Rhizobium interaction.

The nitrogenase reaction requires about 28 mol. of A TP per mol. of N₂ utilized. It has been calculated that recycling 1.28 mol. of H₂ is equivalent to 2.56 mol. of ATP which means that about 9 1% of the 28 mol. of ATP could be recovered for utilization in reducing N₂ to NH₃ by Hup⁺ strains which otherwise would have been wasted in H₂ evolution by Hup^- strains. These assumptions are open to further investigations and precise elucidation.

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