Question

Which of the following is iron in the heme group in the ${Fe}^{3+}$ state?
(a)Oxyhaemoglobin
(b)Methaemoglobin
(c)Carbaminohaemoglobin
(d)Haemoglobin without oxygen

Answer 1

Hint: In normal haemoglobin, the iron in the heme group is in ferrous form or ${Fe}^{2+}$ state. This iron is oxidized to a ferric state ${Fe}^{3+}$. This form of haemoglobin cannot bind to oxygen. This form of haemoglobin is bluish chocolate-brown in colour.

Complete answer:
A form of metalloprotein in the haemoglobin, in which the iron is in the ferric state is called Methaemoglobin. It is generally produced in human blood in trace amounts, but when it is present in excess, the blood becomes abnormally dark bluish brown. This form of haemoglobin cannot carry oxygen to the tissues as it does not bind to oxygen.

Additional Information: -In normal conditions, 2 percent of a person’s haemoglobin is methaemoglobin and any higher percentage may be genetic or due to exposure to various chemicals.
-A higher level of methaemoglobin will lead to the pulse oximeter reading closer to 85 percent irrespective of the true oxygen saturation.
-An abnormal increase in the percentage of methaemoglobin will increase the oxygen-binding affinity of the normal haemoglobin which results in a decreased unloading of the oxygen at tissue sites.
-Depending upon the concentration of methaemoglobin, it may lead to a medical condition known as the methemoglobinemia.
So, the correct answer is, “Methaemoglobin”

Note: -Methemoglobinemia is characterized by an elevated amount of methaemoglobin in the blood which presents itself as headache, dizziness, shortness of breath, nausea, and cyanosis or bluish appearance of skin.
-Blue baby syndrome is a condition in which the oxygen transport in babies is affected which results in the blueness of the skin of the babies. One of the causes of this condition may be elevated to methaemoglobin levels.