Biochemical evidence that leghaemoglobin genes are present in the soybean but not in Rhizobium genome

LEGHAEMOGLOBIN (Lb), a haem protein with structural and functional similarities to animal myoglobin 1 , is found uniquely in legume root nodules,the sites of nitrogen fixation which form during symbiotic association between legumes and soil bacteria of the genus Rhizobium . Alhough in certain conditions free-living Rhizobium can express nitrogenase activity in the absence of Lb (see, for example, ref. 2), the presence of the protein seems to be required for the development of nitrogenase activity by Rhizobium bacteroids within legume root nodule cells. Lb probably functions by transporting oxygen to Rhizobium bacteroids, at the same time maintaining a low partial pressure of oxygen to protect nitrogenase from oxygen-inactivation.