Question

Part of the conformational change in hemoglobin is associated with:

	a.	a change in valency of the heme iron from +2 to +3.
	b.	binding of a proton to an aspartic acid side chain when oxygen is released and release of the proton when oxygen is bound.
	c.	narrowing of the space between the beta chains in the hemoglobin tetramer when oxygen dissociates from the protein.
	d.	extrusion of tyrosine side chains near the C-termini from binding sites on all four subunits when oxygen is bound.
	e.	loss of the heme irons when the tetramer is dissociated into monomers.

Answer 1

A change in velocity of the gene iron from +2 to +3. Iron in Fe2+ state binds oxygen reversibly; when it dissociates from oxygen it becomes Fe3+. Hb exists in two confirmations : R state and T state. Oxygen binds with much higher affinity in R state. Oxygen binding stablized the R state.

There is no binding of a proton to an aspartic acid side when oxygen is released or vice versa although changes in ionic interaction takes place but not specifically with aspartic acid.

Each monomers has its own heme ions so, hb has 4 iron that can bound to 4 oxygen molecule and no loss of the heme irons when the tetramer is dissociates into monomers.

There is interplay of proximal and distal histidine while oxygen binding takes place and no extrusion of tyrosine side chain near the C-termini from binding sites on all four subunits.