Question

What is leghemoglobin?

Answer 1

Hint: Leghemoglobin has closed structural similarity with haemoglobin. It is also red in colour. It is found in the root nodules of leguminous plants.

Complete Answer:
- Leghemoglobin is an oxygen carrier and hemoprotein. It is found in the nitrogen-fixing root nodules of the legumes. It is produced by the bacteria in response to the symbiotic relationship between the plant and the bacterium.
- The roots that do not form nodules do not contain leghemoglobin. The plant expresses the synthesis of heme protein in the nodule.
- The Rhizobium bacteria is present in the root nodules of the leguminous plants. They help in fixing atmospheric nitrogen by the help of nitrogenase . This nitrogenase is sensitive to oxygen.
- The leghemoglobin buffers the oxygen concentration in the plant so that the nitrogenase activity can properly function.
- Plants like casuarina produce leghemoglobin in their root nodules.

Additional information: Hemoglobin and leghemoglobin are evolved from common ancestors. Both are made up of heme protein bound to iron. Hemoglobin and leghemoglobin have similar oxygen binding capacity. They both differ in the amino acid chain. The oxygen binding capacity of leghemoglobin is more than that of animal haemoglobin.
It is used as an ingredient in some plant based meat substitute.

Note: Leghemoglobin is an oxygen carrying red pigment. It has a high affinity for oxygen. The leghemoglobin protects the nitrogenase enzyme from denaturation due to oxygen. At the same time it provides sufficient oxygen to bacteria for its respiration. Thus, maintaining an oxygen buffer.