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In living organisms, because methemoglobin (MetHb) is unable to bind oxygen, it must be reduced to hemoglobin (Hb) through the action of the soluble isoform of cytochrome b5 reductase. Overall, the mechanics of this reaction include electron transfer through oxidation steps, which can be accomplished through a couple of different mechanisms ...
Spontaneously formed methemoglobin is normally reduced (regenerating normal hemoglobin) by protective enzyme systems, e.g., NADH methemoglobin reductase (cytochrome-b5 reductase) (major pathway), NADPH methemoglobin reductase (minor pathway) and to a lesser extent the ascorbic acid and glutathione enzyme systems. Disruptions with these enzyme ...
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.
Cytochrome b5 reductase is involved in the transfer of reducing equivalents from the physiological electron donor, NADH, via an FAD domain to the small molecules of cytochrome b5. It's also heavily involved in many oxidation and reduction reactions, such as the reduction of methemoglobin to hemoglobin. [10]
EC 1.6.2.2 cytochrome-b 5 reductase. NADH + H + + 2 ferricytochrome b 5 → NAD + + 2 ferrocytochrome b 5. EC 1.10.2.1 L-ascorbate—cytochrome-b 5 reductase. L-ascorbate + ferricytochrome b 5 → monodehydroascorbate + ferrocytochrome b 5. EC 1.14.18.2 CMP-N-acetylneuraminate monooxygenase. CMP-N-acetylneuraminate + 2 ferrocytochrome b 5 + O 2 ...
Additionally, the oxygen that is already bound is held more tightly to the hemoglobin due to a higher affinity, resulting in less oxygen delivery. A methemoglobin level > 1.5 g/dL causes cyanosis. The most common congenital cause is a deficiency in the enzyme cytochrome b5 reductase which reduces methemoglobin in the blood. [22]
It works similarly to finasteride by inhibiting the 5 alpha-reductase enzyme, which helps block DHT to some degree. Our thickening shampoo includes saw palmetto as a key ingredient.
The principal biological role of cytochrome b 5 is reduction of methemoglobin, so cytochrome b 5 deficiency can also result in elevated methemoglobin levels and/or methemoglobinemia, similarly to deficiency of cytochrome b 5 reductase (methemoglobin reductase). [1]