5. The blood parasite Dicrocoelium dendriticum expresses a hemoglobin protein th

Question

5. The blood parasite Dicrocoelium dendriticum expresses a hemoglobin protein that is similar in sequence to human hemoglobin. D. dendriticum hemoglobin (Da Hb binds oxygen with much higher affinity than human hemoglobin. In contrast to human hemoglobin, research has shown that hemoglobin does not form quarternary structure, it exists only as a monomer in solution. The p50 value for DdHb varies widely with pH (Smit, J. et al. (1986). Eur. J. Biochem. 155, 231-237.). pH p50 mmH 4.0 0.016 8.0 0.15

Explanation / Answer

Dicrocoelium dendriticum haemoglobin has dioxygen affinity that is being determined as a function of pH using thin-layer diffusion technique.During this technique the oxygen dissociation and association curves Hill coefficients h equal 1 are obtained. Ultracentrifugation process concludes that this haemoglobin is monomeric irrespective of pH and ligation state. Thus, Dicrocoelium haemoglobin is a non-cooperative monomer having highest 0 affinity and its half-saturation pressure, p50 value ranges at 25°C from 0.016 mm Hg to 0.15 mm Hg (2.13-20.0 Pa) depending on pH.It shows an acid Bohr effect only and log p50 versus pH plot (Bohr effect curve) will be shown by a large amplitude.Thus, both the alkaline and the acid Bohr effect arise from a single Bohr group complex -salt bridge.

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