Dimer-tetramer transition in hemoglobins from Liophis miliaris--I. Effect of organic polyphosphates.

Hemoglobin from the water-snake Liophis miliaris in the stripped form presents high oxygen affinity of about P50 = 1 mmHg and Hill coefficient of about 1.0 at pH from 6.8 to 8.5. In the presence of ATP such values become P50 = 20 mmHg and nH about 2.0, respectively, at low pH from 6.5 to 7.5. When the pH increases an abrupt decrease of both P50 and nH values occurs falling close to those found for the stripped hemoglobin. Gel-filtration in Sephadex G-100 equilibrated with 0.05 M Tris-HCl buffer containing 1 mM EDTA of the stripped hemoglobin show the presence of only one component of mol. wt of about 32,500 dt similar to the dimer of human hemoglobin A. The deoxy form of the dimer previously treated with ATP and placed on Sephadex column in the same condition but containing 1 mM IHP emerges as tetramer with mol. wt similar to that found for human hemoglobin, i.e. of about 65,000 dt. Results of the multiplicity of the snake hemoglobin, as well as the large alkaline Bohr effect in the presence of ATP previously reported, seems to be inconsistent due to the dimer-tetramer transition that occurs when ATP is bound to the stripped hemoglobin. A molecular mechanism involving the dimer-tetramer transition is proposed to described the oxygen transport in these animals.