HÆMOGLOBIN AND NITROGEN FIXATION IN THE ROOT NODULES OF LEGUMINOUS PLANTS

Abstract

IT has been shown by Kubo¹ that the root nodules of leguminous plants contain a hæmoprotein compound resembling hæmoglobin and probably acting as a store as well as a carrier of oxygen. The hæmatin nature of this pigment was confirmed by Burris and Haas², who believed, however, that it was not a hæmoglobin-like compound which could undergo oxygenation, but rather an oxido-reduction catalyst in which the iron changes its valency. That this pigment is a true hæmoglobin was demonstrated by Keilin and Wang³, who purified it and found that : (1) it forms a perfectly reversible compound with molecular oxygen ; (2) it has a high affinity for oxygen, the p50 at 15° being less than 0.1 mm. mercury ; and (3) the relative affinity of this pigment for oxygen and carbon monoxide in terms of the equilibrium constant K = [HbCO] [p02]/[Hb02] PpCO] is about 37 at 15° C. They also determined the spectrophotometric absorption curves of this haemoglobin and of its compounds with oxygen and carbon monoxide.