Leghemoglobin

It was originally thought that the heme prosthetic group for plant leghemoglobin was provided by the bacterial symbiont within symbiotic root nodules.

[3][4][5][6][7][8][9][10] In plants colonised by Rhizobium, such as alfalfa or soybeans, the presence of oxygen in the root nodules would reduce the activity of the oxygen-sensitive nitrogenase, which is an enzyme responsible for the fixation of atmospheric nitrogen.

Leghemoglobin is shown to buffer the concentration of free oxygen in the cytoplasm of infected plant cells to ensure the proper function of root nodules.

That being said, nitrogen fixation is an extremely energetically costly process, so aerobic respiration, which necessitates high oxygen concentration, is necessary in the cells of the root nodule.

Without a hydrogen bond fixing the orientation of the proximal histidine side chain the imidazole ring can occupy a staggered conformation between pyrrole nitrogen atoms and can readily move upward to the heme plane.

[17] Heme groups are the same in all known leghemoglobins, but the amino acid sequence of the globin differs slightly depending on bacterial strain and legume species.

In legume, SNF takes place in specialized organs called nodules which contain bacteroids, or nitrogen fixing rhizobia.

The induction of nodule-specific plant genes, which include those that encode for symbiotic leghemoglobins (Lb), accompany nodule development.

Leghemoglobins make the essential contribution of establishing low free-oxygen concentrations while keep a high energy status in cells.

[12] Impossible Foods asked the American FDA for their approval to use recombinant soy leghemoglobin in meat alternatives as an analog of meat-derived hemoglobin.