The concentration and distribution of haemoglobin in the root nodules of leguminous plants.

All legume nodules which are actively fixing nitrogen contain a red pigment. This pigment escaped attention until Pietz (1938) suggested that it was identical with dihydroxyphenylalanine (Dopa), the red intermediate in the enzymic oxidation of tyrosine. Kubo (1939), however, prepared a crude extract of the pigment and from its spectroscopic behaviour identified it as a haemoprotein possessing properties very similar to those of haemoglobin. Burris & Haas (1944) stated that the pigment was not a haemoglobin but a haemoprotsin oxidationreduction catalyst. However, Keilin & Wang (1945), working on an extract about 50% pure, were able to confirm the haemoglobin-like nature of the pigment by showing that it was capable of completely reversible oxygenation and deoxygenation; they determined the absorption spectra ofthe oxygenated and reduced haemoglobin and those of some of its derivatives. Keilin & Wang suggested that the