Acid Bohr effect of a monomeric haemoglobin from Dicrocoelium dendriticum. Mechanism of the allosteric conformation transition.
The dioxygen affinity of Dicrocoelium dendriticum haemoglobin was determined as a function of pH with a thin-layer diffusion technique. From the oxygen dissociation and association curves Hill coefficients h equal 1 were obtained throughout. Ultracentrifugation studies prove this haemoglobin to be monomeric irrespective of pH and ligation state. Thus, Dicrocoelium haemoglobin is a non-cooperative monomer. It has the highest O2 affinity so far known for any monomeric haemoglobin: its half-saturation pressure, p50 value, ranges at 25 degrees C from 0.016 mm Hg to 0.15 mm Hg (2.13-20.0 Pa) dependent on pH. Dicrocoelium haemoglobin shows an acid Bohr effect only and as such it constitutes a new class of haemoglobins. Its log p50 versus pH plot (Bohr effect curve) is characterized by a large amplitude, delta log p50 = 0.96, and an inflection point (Bohr effect pK) at pH 5.0. A model for the acid Bohr effect of D. dendriticum haemoglobin is proposed. By generalization, both the alkaline and the acid Bohr effect in various monomeric haemoglobins may arise from a single Bohr group complex (salt bridge).
D000495:Allosteric Site; D000818:Animals; D001665:Binding Sites; D002683:Chironomidae; D004013:Dicrocoelium; D006454:Hemoglobins / Q000302:isolation & purification / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008961:Models, Structural; D010100:Oxygen / Q000378:metabolism; D011487:Protein Conformation; D012756:Sheep
D006454:Hemoglobins; D010100:Oxygen