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In these tissues, hemoglobin absorbs unneeded oxygen as an antioxidant, and regulates iron metabolism. [12] Excessive glucose in the blood can attach to hemoglobin and raise the level of hemoglobin A1c. [13] Hemoglobin and hemoglobin-like molecules are also found in many invertebrates, fungi, and plants. [14]
Binding of oxygen to a heme prosthetic group. Heme (American English), or haem (Commonwealth English, both pronounced /hi:m/ HEEM), is a ring-shaped iron-containing molecular component of hemoglobin, which is necessary to bind oxygen in the bloodstream. It is composed of four pyrrole rings with 2 vinyl and 2 propionic acid side chains. [1]
Hemoglobin A (HbA), also known as adult hemoglobin, hemoglobin A1 or α 2 β 2, is the most common human hemoglobin tetramer, accounting for over 97% of the total red blood cell hemoglobin. [1] Hemoglobin is an oxygen-binding protein, found in erythrocytes , which transports oxygen from the lungs to the tissues. [ 2 ]
When hemoglobin is not attached to oxygen (and is then called deoxyhemoglobin), the Fe 2+ ion at the center of the heme group (in the hydrophobic protein interior) is in a high-spin configuration. It is thus too large to fit inside the porphyrin ring, which bends instead into a dome with the Fe 2+ ion about 55 picometers above it. In this ...
Hemoglobin has an oxygen binding capacity between 1.36 and 1.40 ml O 2 per gram hemoglobin, [23] which increases the total blood oxygen capacity seventyfold, [24] compared to if oxygen solely were carried by its solubility of 0.03 ml O 2 per liter blood per mm Hg partial pressure of oxygen (about 100 mm Hg in arteries).
This amount of carbaminohemoglobin formed is inversely proportional to the amount of oxygen attached to hemoglobin. Thus, at lower oxygen saturation, more carbaminohemoglobin is formed. These dynamics explain the relative difference in hemoglobin's affinity for carbon dioxide depending on oxygen levels known as the Haldane effect. [2]
Hemoglobin and myoglobin are examples of hemeproteins that respectively transport and store of oxygen in mammals and in some fish. [9] Hemoglobin is a quaternary protein that occurs in the red blood cell, whereas, myoglobin is a tertiary protein found in the muscle cells of mammals.
After being carried in blood to a body tissue in need of oxygen, O 2 is handed off from the heme group to monooxygenase, an enzyme that also has an active site with an atom of iron. [9] Monooxygenase uses oxygen for many oxidation reactions in the body. Oxygen that is suspended in the blood plasma equalizes into the tissue according to Henry's law.