Leghemoglobin
The oxygen carrier
leghemoglobin (also
legoglobin) is a
hemoprotein found in the
nitrogen-fixing root nodules of
leguminous plants. It is produced by legumes in response to the roots being infected by the nitrogen-fixing bacterium,
rhizobium, as part of the
symbiotic interaction between plant and bacterium: roots uninfected with Rhizobium do not synthesise leghemoglobin. Leghemoglobin has close chemical and structural similarities to
hemoglobin, and, like hemoglobin, is red in colour. The protein is a product of both
plant and the
bacterium; the
apoprotein is produced by the plant and the
heme (an iron atom bound in a
porphyrin ring) is produced by the
bacterium.
In plants infected with Rhizobium, (such as
alfalfa or
soybeans), the presence of
oxygen in the root nodules would reduce the activity of the oxygen-sensitive
nitrogenase. Leghemoglobin buffers the concentration of free
oxygen in the
cytoplasm of infected plant cells to ensure the proper function of root nodules.
See also: hemoglobin, myoglobin*
Chemistry of leghaemoglobin
