Question

biochem question:

At the pO2 in ACTIVE muscle tissue, would Mb or Hb be predicted to have the higher Kd value? Explain, correlating with function of the protein.

Would a protein with only tertiary structure ever display cooperative binding?

Answer 1

Kd is the dissociation constant, which shows that the amount of free or dissociated hemoglobin concentration from its total hemoglobin concentration.

To understand the question, we need to know the oxygen binding curve of hemoglobin and myoglobin. We can see from the figure given below that the oxygen binding curve of hemoglobin is sigmoidal which means hemoglobin has less affinity for oxygen.

So, when oxygen transported from lung to muscle tissue, where the partial pressure of oxygen is less, hemoglobin dissociated from oxygen and provides it to the tissue. However, myoglobin still maintains an affinity for oxygen and the answer is yes at given partial pressure hemoglobin has higher kd value.

Quaternary structure is made when 2 or more polypeptide is joined together by interaction. In cooperative binding, when ligand bind to subunit, it changes the conformation of another subunit. So, if there is no Quaternary structure, then the cooperative binding will not be possible.