Hemoglobin prosthetic group

Heme (C34H3204N4Fe) represents an iron-porphyrin complex that has a protoporphyrin nucleus. Many important proteins contain heme as a prosthetic group. Hemoglobin is the quantitatively most important hemoprotein. Others are cytochromes (present in the mitochondria and the endoplasmic reticulum), catalase and peroxidase (that react with hydrogen peroxide), soluble guanylyl cyclase (that converts guanosine triphosphate, GTP, to the signaling molecule 3, 5 -cyclic GMP) and NO synthases. 

Let us return to the cases of myoglobin and hemoglobin and recognize something explicitly these two proteins contain a nonprotein constiment. This constituent, or prosthetic group, is heme, a complex polycyclic structure, protoporphyrin IX, containing an atom of iron (as Fe (II) or Fe +) at its center. 

The cases of myoglobin and hemoglobin are not rare. Many enzymes are dependent for their function on the presence of a nonprotein group. For example, cytochrome c also contains a prosthetic group similar, but not identical, to heme, as do a number of other proteins. These are known generically as heme proteins. There is a family of enzymes that contain a flavin group, the flavoproteins. Another family contains pyridoxal phosphate, a derivative of vitamin Be. There are a number of other examples. 

Heme is mainly found in the human organism as a prosthetic group in erythrocyte hemoglobin. Around 100-200 million aged erythrocytes per hour are broken down in the human organism. The degradation process starts in reticuloendothelial cells in the spleen, liver, and bone marrow. 

Hemeproteins are a group of specialized proteins that contain heme as a tightly bound prosthetic group. Examples of hemeproteins include cytochromes, catalase, hemoglobin, and myoglobin. 

An iron porphyrin is the prosthetic group in the oxygen transport and storage proteins, hemoglobin and myoglobin. Consequently there has been much interest in porphyrin complexes, especially of first row transition metals, as model systems for oxygen transport and storage. Much interest has also been shown in metal porphyrins as models for oxidases, in particular cytochrome P-450. 

Hemoglobin has quaternary structure as it is made up of four polypeptide chains two a-chains and two (3-chains (a2 32), each with a heme prosthetic group. Despite little similarity in their primary sequences, the individual polypeptides of hemoglobin have a three-dimensional structure almost identical to the polypeptide chain of myoglobin. 

Binding of oxygen The heme prosthetic group in myoglobin and hemoglobin is made up of a... 

Hemes (Fig. la) are a diverse group of tetrapyrrole pigments, being present as the prosthetic group of both the globins (hemoglobin and myoglobin Topic... 

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