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The structure of cytochrome b5 reductase, the enzyme that converts methemoglobin to hemoglobin. [1]Methemoglobin (British: methaemoglobin, shortened MetHb) (pronounced "met-hemoglobin") is a hemoglobin in the form of metalloprotein, in which the iron in the heme group is in the Fe 3+ state, not the Fe 2+ of normal hemoglobin.
The congenital form of methemoglobinemia has an autosomal recessive pattern of inheritance. Due to a deficiency of the enzyme diaphorase I (cytochrome b5 reductase), methemoglobin levels rise and the blood of met-Hb patients has reduced oxygen-carrying capacity. Instead of being red in color, the arterial blood of met-Hb patients is brown.
Methemoglobin is an oxidized form of hemoglobin attached to a ferric-state iron (Fe3+), which can therefore not carry and deliver oxygen to tissues. [15] The formation of methemoglobin occurs when electrons are not returned to the iron of a normal state hemoglobin, which is not preferred for a functioning organism.
Methemoglobin is also formed in small quantities when the dissociation of oxyhemoglobin results in the formation of methemoglobin and superoxide, O 2 −, instead of the usual products. Superoxide is a free radical and causes biochemical damage, but is neutralised by the action of the enzyme superoxide dismutase.
Hemoglobin Barts (γ 4) – A variant form of hemoglobin, formed by a tetramer of γ chains, which may be present in variants of α thalassemia. Hemoglobin S (α 2 β S 2) – A variant form of hemoglobin found in people with sickle cell disease. There is a variation in the β-chain gene, causing a change in the properties of hemoglobin, which ...
Methemoglobinemia is a condition caused by elevated levels of methemoglobin in the blood. Methaemoglobin is a form of hemoglobin that contains the ferric [Fe 3+] form of iron, instead of the ferrous [Fe 2+] form . Methemoglobin cannot bind oxygen, which means it cannot carry oxygen to tissues.
Heinz body stain of feline blood, showing three distinct Heinz bodies. Heinz bodies appear as small round inclusions within the red cell body, though they are not visible when stained with Romanowsky dyes. They are visualized more clearly with supravital staining [5] [6] (e.g., with new methylene blue, crystal violet or bromocresol green).
The average adult has a blood volume of roughly 5 litres (11 US pt) or 1.3 gallons, [10] which is composed of plasma and formed elements. The formed elements are the two types of blood cell or corpuscle – the red blood cells, (erythrocytes) and white blood cells (leukocytes), and the cell fragments called platelets [12] that are involved in ...