The iron of the heme group in myoglobin: a. is bound to four pyyrol nitrogens, a

Question

The iron of the heme group in myoglobin:

a. is bound to four pyyrol nitrogens, a proximal histidine, and a distal histidine

b. is bound to four pyyrol nitrogens, a distal histidine, and a water molecule

c. is bound to four pyyrol nitrogens, a distal histidine, and an oxygen molecule

d. is bound to four pyyrol nitrogens, a distal histidine, and an oxygen molecule bound to proximal histidine

e. is bound to four pyyrol nitrogens, a proximal histidine, and an oxygen molcule bound to distal histidine

Explanation / Answer

Answer

The iron of the heme group in myoglobin:

e. is bound to four pyyrol nitrogens, a proximal histidine, and an oxygen molcule bound to distal histidine.

In deoxy-hemoglobin, four of the coordinated sites of iron are occupied by nitrogens of porphyrin ring. The fifth site is occupied by Histidine residue (called proximal histidine) of globin. The sixth position is occupied by weakly bonded water molecule. Hence some authors tend to report Fe(II) ion in deoxy form as pentacoordinated. Deoxy-hemoglobin is said to be in T-state.

On the opposite side of the proximal histidine, there is one more histidine group (called distal histidine) placed near the iron ion. It forces the binding of dioxygen in "end on bent" confirmation.

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