Question

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Answer 1

Myoglobin (symbol Mb or MB) is an iron- and oxygen-binding protein found in the muscle tissue of vertebrates in general and in almost all mammals. It is not related to hemoglobin, which is the iron- and oxygen-binding protein in blood, specifically in the red blood cells.

Hemoglobin and Myoglobin, both are oxygen binding proteins however, they differ largely in their function as:

Myoglobin is a monomeric protein and binds molecular oxygen and carry to muscle tissues. Muscle cells use myoglobin to exchange oxygen during active respiration. Myoglobin consists of 8 right handed α-helices and each protein molecule contains one heme prosthetic group and each heme residue contains one central coordinately bound iron atom. Oxygen is bound directly to the iron atom of the heme prosthetic group. It transport and store oxygen. Binds oxygen more tightly and easily.

Hemoglobin is a tetrameric protein and binds molecular oxygen on RBCs. Being a tetramer it binds four oxygen molecules and distribute them throughout the whole body. It serves to deliver oxygen needed for cellular metabolism and removes the resulting waste product, carbon dioxide from the body tissues. Human hemoglobin is composed of two α (alpha) and two β (beta) subunits. Each α-subunit has 144 residues, and each β-subunit has 146 residues. Structural characteristics of both α (alpha) and β (beta) subunits are similar to myoglobin. It transport oxygen. Concentration of hemoglobin is high in RBCs. Binds oxygen loosely and with difficulty. Hemoglobin in its deoxygenated state has a low affinity for oxygen compared to myoglobin. When oxygen is bound to the first subunit of hemoglobin it leads to subtle changes to the quaternary structure of the protein. This in turn makes it easier for a subsequent molecule of oxygen to bind to the next subunit. Thus, with the initial oxygen binding to a subunit, the remaining unbound subunits become more receptive to oxygen. This phenomenon is called an allosteric (through space) interaction/ cooperativity and is clearly illustrated in the sigmoidal curve for oxygen binding to hemoglobin at neutral pH