The oxygen-binding hemoprotein was first recognized in root nodules by Kubo in 1939. Leghaemoglobin (Lb) occurs in the infected cells of legume root nodules. The concentration ranges l-3mg per g fresh weight depending on the plant species. Heme synthesis for Lb seems to be a bacterial property whereas, the apoprotein (globin) is coded for by the plant DNA and thus a well evolved coexistence mechanism between the host and the bacterium is seen in legume root nodules. Lb facilitates oxygen diffusion across the nodule into the nitrogen fixing bacteriods to support oxidation and at the same time ensures the oxygen sensitive nitrogenase activity without damage.
Haemoglobin reacts with pyridine in strong alkali to produce hemochrome. The hemochrome is measured at 556nm.
» Diluent Buffer: 0.1M sodium/potassium phosphate buffer (pH 7.4).
» Alkaline Pyridine Reagent: Dissolve 0.8g NaOH in 50mL water and cool. Add 33.8mL of pyridine (33.2g), dissolve and dilute to 100mL with water. This produces 4.2M pyridine in 0.2M NaOH.
» Sodium Dithionite: Grind finely and store in small stoppered tubes in a desiccator.
» Potassium Hexacyanoferrate
(The calculation is based upon the equation E = 23.4 X 103 mol-1 cm-1)
Appleby, C A and Bergersen, F J (1980) In: Methods for Evaluating Biological Nitrogen Fixation (Ed. Bergersen F J) John Wiley and Sons New York p 315.
© 2018 Biocyclopedia | All rights reserved.