Question

The blood parasite Dicrocoelium dendriticum expresses a hemoglobin protein that is similar in sequence to human hemoglobin. D. dendriticum hemoglobin (Dd Hb) binds oxygen with much higher affinity than human with 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 varies widely with pH (Smit, j.et al. (1986). Eur. J. Biochem. 155, 231-237.). a. Do you expect to show cooperative oxygen binding, given the information above? Explain, and clearly define cooperative oxygen binding as part of your answer. b. Based on the information above, sketch the oxygen binding curves for Dd Hb at pH 4.0 and pH 8.0 on a single set of axes. Consider shape and position of each curve. c. Do you expect Dd Hb to show regulation of oxygen binding, given the information above? Explain, and clearly define binding as part of your answer. d. As in human Hb, we can propose a model where Dd Hb has two different conformational states: a state with high affinity for oxygen and a state with low affinity for oxygen. For Dd Hb, which state is stabilized by the event? Explain your answer using data provided.

Answer 1

A. ANS:

Cooperative Binding explains how the ligand changes and interact with other ligands. In monomeric structure cooperative oxygen binding does not taken placed. Hemoglobin is a tetrameric unit in which it had 2 alpha and 2 beta chains. In hemoglobin cooperative Binding oxygen molecule binds to the one subunit and it alters the affinity for oxygen in adjacent subunits. This phenomenon is known as an allosteric effect. Hemoglobin can either in T State (Tense state, Inactive form) or R State (Relaxed state, Active form)

In the T state ions are paired with the hemoglobin and stabilize the T state. In hemoglobin R state oxygen molecule binds tightly with higher affinity.

Conformational Change in Hemoglobin are happens due to the α and β subunit dimers slide past one another, rotate slightly and narrow the pocket between β subunits.

B. ANS:

C. ANS: In hemoglobin cooperative Binding oxygen molecule binds to the one subunit and it alters the affinity for oxygen in adjacent subunits. This phenomenon is known as an allosteric effect. So we can expect Dd Hb to show allosteric regulation of oxygen binding. Hemoglobin oxygen binding is influenced by several factors such as carbondioxide, 2,3 diphosphoglycerate, temperature and pH.

D. ANS: In haemoglobin bohr affect can increase in PCO2 there is an increase in oxygen dissociation. This affect leads to shift the curve right. Decrease in pH has got low affinity for oxygen and thus promotes oxygen delivery at tissues which release co2 on metabolism. hydrogen ions from dissociation of carbonic acid compete for space taken up by the oxygen molecules on Hb molecule. when CO2 is present , hydrogen ions displace the oxygen on the haemoglobin .

Bohr effect: Haemoglobin oxygen binding affinity is inversely related both to acidity and to the concentration of carbon dioxide.

             Co2+H2o -----> H2Co3+H