The amino acid sequence of hemoglobin I from nitrogen-fixing root nodules of the Casuarina glauca-Frankia symbiosis has been determined. The protein is composed of 151 amino acids including a single cysteine, a residue not found in the leghemoglobins. The molecular mass, including heme, is calculated to be 17856 Da. C. glauca hemoglobin I shows extensive sequence homology (43–52%) with other plant hemoglobins and this provides further evidence that hemoglobins from distant plant genera and animal hemoglobins share a common evolutionary origin.
