Leghemoglobin

Leghaemoglobin called globins, which occur in the nitrogen-fixing root nodules of legumes ( Leguminosae ). It formed several paralogous isoforms that contain 145-150 amino acids.

Function

If a root infected with nitrogen-fixing rhizobia, the plant is stimulated to produce leghemoglobin. Root parts which are not infected by rhizobia that produce no leghaemoglobin. Leghaemoglobin is evolutionarily very closely related to myoglobin and hemoglobin and has a very similar tertiary structure. It has as other globular heme proteins the ability to reversibly bind oxygen. Leghaemoglobin thus ensures that there is in the root nodules, a very low concentration of free oxygen. This is essentially important for a functioning symbiosis with nodule bacteria. The nitrogenase complex of the bacteria is sensitive to oxygen maximum organization, as it can inactivate the complex, and thus the nitrogen fixation even in low concentrations.

Leghaemoglobin was about ten times as high affinity to oxygen than the β - chain of human hemoglobin. This affinity causes the oxygen concentration in the tissue and in the bacteria is low enough so that the nitrogenase is not disabled, the bacteria and the plant tissue but can still obtain enough oxygen for cell respiration. The operation of leghaemoglobin is therefore directly comparable to that of hemoglobin.

Previously, it was assumed that all of the protein is synthesized by the plant. However, O'Brien et al were able to show that both plant and bacteria are involved in the synthesis of the protein. The plant produces the apoprotein synthesized the heme during the bacterium. Other studies suggest even suggest that a part of the globin is produced by the bacteria.

Evolutionary tree

Analyses of the amino acid sequence of the globins shows the relationship of leghaemoglobin with myoglobin and hemoglobin. The first splitting of the globins in the two classes Leghämoglobine and hemoglobins took place before about 800 million years ago.