Hemoglobin in blood system

Hemoglobin is a two-way respiratory carrier, transporting oxygen from the lungs to the tissues and facilitating the return transport of carbon dioxide.

Hemoglobin is made up of small molecules called amino acids. Each hemoglobin molecule is made up of four heme groups surrounding a globin group, forming a tetrahedral structure. All hemoglobins carry the same prosthetic heme group iron protoporphyrin IX associated with a polypeptide chain of 141 (α) and 146 (β) amino acid residues. The porphyrin ring is wedged into its pocket by a phenylalanine of its polypeptide chain.

The heme part is synthesized in a series of steps in the in a series of steps in the mitochondria and the cytosol of immature red blood cells, while the globin protein parts are synthesized by ribosomes in the cytosol.

Hemoglobin increases O2 solubility in blood by about a hundredfold. This means that without hemoglobin, in order to provide sufficient oxygen to the tissues, blood would have to make a complete circuit through the body in less than a second, instead of the minute that it actually takes. Iron must be in ferrous state which can binds to oxygen and form oxy hemoglobin.

Hemoglobin picks up oxygen in the lungs, circulates through the bloodstream to the muscles (and other tissues), and drops off oxygen there. Myoglobin picks up the oxygen and delivers it to the mitochondria, where it is used to oxidize fuel molecules.
Hemoglobin in blood system

Destruction of hemoglobin

Hemoglobin is a protein based component and is the main part of red blood cells. It is a large molecule made up of proteins and iron. It consists of four folded chains of a protein called globin, designated alpha 1 and 2, and beta 1 and 2. Each of these globin molecules is bound to a red pigment molecule called heme, which contains an ion of iron (Fe2+).

When red blood cells are delivered from the bone marrow into the circulatory system, they normally circulate an average of 120 days before being destroyed.

When red blood cells burst and release their hemoglobin, the hemoglobin is phagocytized almost immediately by macrophages in many parts of the body, but especially by the Kupffer cells of the liver and macrophages of the spleen and bone marrow.

During the next few hours to days, the macrophages release iron from the hemoglobin and pass it back into the blood, to be carried by transferring either to the bone marrow for the production ofnew red blood cells or to the liver and other tissues for storage in the form of ferritin.

Most of the heme degradation in biological systems occurs in two different pathways: an enzymatic pathway that requires the heme oxygenase system; or a nonenzymatic pathway that requires the interaction with reactive oxygen species (ROS), reducing agents, or xenobiotics.

*In the enzymatic pathway, heme oxygynase catalyzes heme cleavage and subsequently releases the heme iron in the ferrous form, and in a specific manner it eliminates the carbon-methene bridge of heme as CO to form bilivedrin.

*In the non-enzymatic pathways, ROS such as superoxide (O2−), hydrogen peroxide (H2O2), and hypochlorous acid (HOCl) can mediate heme destruction unselectively at any position of the heme double bonds.

Destruction of hemoglobin 

What are the components of hemoglobin?

Hemoglobin is the protein that transports oxygen (O2) in human blood from the lungs to the tissues of the body. A hemoglobin molecule is composed of four polypeptide globin chains. Each contains a heme moiety which has an organic part (a protoporphyrin ring made up of four pyrrole rings) and a central iron ion in the ferrous state (Fe2+).

Heme synthesis occurs both in cytosol and in mitochondria of erythrocytes. Protoporphyrin is synthesized from the condensation of glycine and succinyl coenzyme A, eight molecules of each being required to form a linear tetrapyr-role molecule, which finally cyclizes into the protoporphyrin ring. The protoporphyrin then binds to a Fe2+ ion to form heme.

Each heme group contains an iron atom that is able to bind to one oxygen (O2) molecule. Because hemoglobin contains four heme groups, each hemoglobin protein can bind four oxygen molecules.

Fe2+ is a major component of hemoglobin that carries oxygen to all parts of the body. Fe2+ also has a critical role within cells assisting in oxygen utilization, enzymatic systems, especially for neural development, and overall cell function everywhere in the body.
What are the components of hemoglobin?

Hemoglobin molecule

The hemoglobin is the intensely colored pigment which imparts the red color o the blood; hemoglobin is the most abundant blood protein in man, and represents more than 95% of the soluble protein content of the erythrocytes.

The hemoglobin molecule is composed of two parts, heme and globin, The globin portion of a hemoglobin molecule contains four proteins, two α-chains, and two β-chains. Both the α- and β-chains of hemoglobin are very similar to the myoglobin chain. The α -chain is 141 residues long, and the β -chain is 146 residues long: for comparison, the myoglobin chain is 153 residues long.

The heme portion of hemoglobin molecules contains iron. Iron makes up 0.35% of the hemoglobin molecule and its porphyrin moiety an additional 3,5% with the remainder consisting of protein.

Each of hemoglobin has a molecular weight of approximately 64,000 and an elliptical shape with molecular dimensions of approximately 63 x 55 x 50 A. Hemoglobin molecules continually release and bind oxygen molecules as they travel through the circulatory systems. At areas of high levels of oxygen concentration, the hemoglobin molecules reabsorb the oxygen they release.
Hemoglobin molecule

Hemoglobin as a carrier

Oxygen is carried in the blood mainly bound to hemoglobin; a minor fraction is dissolved in the plasma. Hemoglobin releases the oxygen that sustains every body cell.

There are about 2.5 billion red blood cells circulating at any one time. With some 280 million molecules of hemoglobin packed inside them – each of them capable of carrying four oxygen molecules.

The maximum oxygen that can be bound to the hemoglobin in the blood is the oxygen capacity. One gram of hemoglobin theoretically can carry up to 1.39 mL of oxygen. More commonly an oxygen binding capacity of 1.34 to 1.36 mL oxygen per gram hemoglobin is accepted.

Disturbances in oxygen uptake in the lungs, or in supply of adequate amounts of oxygen to the tissues, are common features of many congenital heart lesions.

Red blood cells can carry much larger quantities of carbon dioxide than they can carry oxygen. During rest 100 mL of blood carries an average of 4 mL of carbon dioxide from the tissue to the lungs.

While the oxygen-carrying hemoglobin imparts a red color to the blood, on its return to the lungs hemoglobin loaded with carbon dioxide loses its bright color and assumes a dark red-dish shade, akin to purple.
Hemoglobin as a carrier